Method and apparatus for plasma dicing a semi-conductor wafer

ABSTRACT

The present invention provides a method for plasma dicing a substrate. The method comprising: providing a process chamber having a wall; providing a plasma source adjacent to the wall of the process chamber; providing a work piece support within the process chamber; placing the substrate on a carrier support to form a work piece; providing an intermediate ring interposed between the substrate and the frame; loading the work piece onto the work piece support; generating a plasma through the plasma source; and etching the work piece through the generated plasma.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority from and is related to commonly ownedU.S. Provisional Patent Application Ser. No. 61/452,450 filed Mar. 14,2011, entitled: Apparatus for Plasma Dicing a Semi-conductor Wafer, thisProvisional patent application incorporated by reference herein. Thisapplication is a continuation-in-part of co-pending patent applicationSer. No. 13/412,119 filed on Mar. 5, 2012, entitled: Method andApparatus for Plasma Dicing a Semi-conductor Wafer, the contents ofwhich are incorporated herein.

FIELD OF THE INVENTION

The invention relates to the use of an apparatus for the formation ofindividual device chips from a semi-conductor wafer, and in particularto an apparatus which uses plasma etching to separate the wafer intoindividual die.

BACKGROUND

Semiconductor devices are fabricated on substrates which are in the formof thin wafers. Silicon is commonly used as the substrate material, butother materials, such as III-V compounds (for example GaAs and InP) arealso used. In some instances (for example, the manufacture of LED's) thesubstrate is a sapphire or silicon carbide wafer on which a thin layerof a semi-conducting material is deposited. The diameter of suchsubstrates range from 2 inches and 3 inches up to 200 mm, 300 mm, and450 mm and many standards exist (e.g., SEMI) to describe such substratesizes.

Plasma etching equipment is used extensively in the processing of thesesubstrates to produce semi-conductor devices. Such equipment typicallyincludes a vacuum chamber fitted with a high density plasma source suchas Inductively Coupled Plasma (ICP) which is used to ensure high etchrates, necessary for cost-effective manufacturing. In order to removethe heat generated during the processing, the substrate is typicallyclamped to a temperature controlled support. A pressurized fluid,typically a gas such as Helium is maintained between the substrate andthe support to provide a thermal conductance path for heat transfer. Amechanical clamping mechanism, in which a downward force is applied tothe top side of the substrate, may be used, though this may causecontamination due to the contact between the clamp and the substrate.Work piece bowing may also occur when using a mechanical clamp, sincecontact is typically made at the edge of the work piece and apressurized fluid exerts a force on the back of the work piece. Morefrequently an electrostatic chuck (ESC) is used to provide the clampingforce.

Numerous gas chemistries appropriate to the material to be etched havebeen developed. These frequently employ a halogen (Fluorine, Chlorine,Bromine, or Iodine) or halogen-containing gas together with additionalgases added to improve the quality of the etch (for example, etchanisotropy, mask selectivity and etch uniformity). Fluorine containinggases, such as SF₆, F₂ or NF₃ are used to etch silicon at a high rate.In particular, a process (Bosch or TDM) which alternates a high ratesilicon etch step with a passivation step to control the etch sidewall,is commonly used to etch deep features into silicon. Chlorine andBromine containing gases are commonly used to etch III-V materials.

Plasma etching is not limited to semiconducting substrates and devices.The technique may be applied to any substrate type where a suitable gaschemistry to etch the substrate is available. Other substrate types mayinclude carbon containing substrates (including polymeric substrates),ceramic substrates (e.g., AlTiC and sapphire), metal substrates, glasssubstrates, and die attach films

To ensure consistent results, low breakage and ease of operation,robotic wafer handling is typically used in the manufacturing process.Handlers are designed to support the wafers with minimal contact, tominimize possible contamination and reduce the generation ofparticulates. Edge contact alone, or underside contact close to thewafer edge at only a few locations (typically within 3-6 mm of the waferedge) is generally employed. Handling schemes, which include wafercassettes, robotic arms and within process chamber fixtures includingthe wafer support and ESC, are designed to handle the standard wafersizes as noted previously.

After fabrication on the substrate, the individual devices (die orchips) are separated from each other prior to packaging or beingemployed in other electronic circuitry. For many years, mechanical meanshave been used to separate the die from each other. Such mechanicalmeans have included breaking the wafer along scribe lines aligned withthe substrate crystal axis or by using a high speed diamond saw to sawinto or through the substrate in a region (streets) between the die.More recently, lasers have been used to facilitate the scribing process.

Such mechanical wafer dicing techniques have limitations which affectthe cost effectiveness of this approach. Chipping and breakage along thedie edges can reduce the number of good die produced, and becomes moreproblematic as wafer thicknesses decrease. The area consumed by the sawbade (kerf) may be greater than 100 microns which is valuable area notuseable for die production. For wafers containing small die (e.g.,individual semiconductor devices with a die size of 500 microns×500microns) this can represent a loss of greater than 20%. Further, forwafers with many small die and hence numerous streets, the dicing timeis increased, and productivity decreased, since each street is cutindividually. Mechanical means are also limited to separation alongstraight lines and the production of square or oblong shaped chips. Thismay not represent the underlying device topology (e.g., a high powerdiode is round) and so the rectilinear die format results in significantloss of useable substrate area. Laser dicing also has limitations byleaving residual material on the die surface or inducing stress into thedie.

It is important to note that both sawing and laser dicing techniques areessentially serial operations. Consequently, as device sizes decrease,the time to dice the wafer increases in proportion to the total dicingstreet length on the wafer.

Recently plasma etching techniques have been proposed as a means ofseparating die and overcoming some of these limitations. After devicefabrication, the substrate is masked with a suitable mask material,leaving open areas between the die. The masked substrate is thenprocessed using a reactive-gas plasma which etches the substratematerial exposed between the die. The plasma etching of the substratemay proceed partially or completely through the substrate. In the caseof a partial plasma etch, the die are separated by a subsequent cleavingstep, leaving the individual die separated. The technique offers anumber of benefits over mechanical dicing:

1) Breakage and chipping is reduced;

2) The kerf dimensions can be reduced to well below 20 microns;

3) Processing time does not increase significantly as the number of dieincreases;

4) Processing time is reduced for thinner wafers; and

5) Die topology is not limited to a rectilinear format.

After device fabrication, but prior to die separation, the substrate maybe thinned by mechanical grinding or similar process down to a thicknessof a few hundred microns, or even less than a hundred microns.

Prior to the dicing process, the substrate is typically mounted on adicing fixture. This fixture is typically comprised of a rigid framethat supports an adhesive membrane. The substrate to be diced is adheredto the membrane. This fixture holds the separated die for subsequentdownstream operations. Most tools used for wafer dicing (saws or laserbased tools) are designed to handle substrates in this configuration anda number of standard fixtures have been established; however, suchfixtures are very different from the substrates which they support.Though such fixtures are optimized for use in current wafer dicingequipment, they cannot be processed in equipment which has been designedto process standard substrates. Thus, current automated plasma etchingequipment is not suitable for processing substrates fixtured for dicingand it is difficult to realize the benefits that plasma etch techniquesshould have for die separation.

Some groups have contemplated using plasma to singulate die from wafersubstrates. U.S. Pat. No. 6,642,127 describes a plasma dicing techniquein which the substrate wafer is first attached to a carrier wafer via anadhesive material, before plasma processing in equipment designed forprocessing silicon wafers. This technique proposes adapting the formfactor of the substrate to be diced to be compatible with standard waferprocessing equipment. While this technique allows standard plasmaequipment to dice the wafer, the proposed technique will not becompatible with standard equipment downstream of the dicing operation.Additional steps would be required to either adapt the downstreamequipment or revert the substrate form factor for standard downstreamequipment.

U.S. Patent Application 2010/0048001 contemplates the use of a waferadhered to a thin membrane and supported within a frame. However, in the2010/0048001 application, the masking process is achieved by adhering amask material to the backside of the wafer and using a laser to definethe etch streets prior to plasma processing. In contrast to standarddicing techniques which singulate the substrate from the front side,this technique introduces additional complex and expensive steps whichmay negate some of the advantages of plasma dicing. It also requires theadditional demand of aligning the backside mask with the front sidedevice pattern.

Therefore, what is needed is a plasma etching apparatus which can beused for dicing a semiconductor substrate into individual die and whichis compatible with the established wafer dicing technique of handling asubstrate mounted on tape and supported in a frame, and which is alsocompatible with standard front side masking techniques.

Nothing in the prior art provides the benefits attendant with thepresent invention.

Therefore, it is an object of the present invention to provide animprovement which overcomes the inadequacies of the prior art devicesand which is a significant contribution to the advancement to the dicingof semiconductor substrates using a plasma etching apparatus.

Another object of the present invention is to provide a method forplasma dicing a substrate, the method comprising: providing a processchamber having a wall; providing a plasma source adjacent to the wall ofthe process chamber; providing a work piece support within the processchamber; placing the substrate on a carrier support to form a workpiece; providing an intermediate ring interposed between the substrateand the frame; loading the work piece onto the work piece support;generating a plasma through the plasma source; and etching the workpiece through the generated plasma.

Yet another object of the present invention is to provide a method forplasma dicing a substrate, the method comprising: providing a processchamber having a wall; providing a plasma source adjacent to the wall ofthe process chamber; providing a work piece support within the processchamber; placing the substrate on a carrier support to form a workpiece; providing an intermediate ring interposed between the substrateand the frame; providing a cover ring between the plasma source and thework piece; loading the work piece onto the work piece support;generating a plasma through the plasma source; and etching the workpiece through the generated plasma.

Still yet another object of the present invention is to provide a methodfor plasma dicing a substrate, the method comprising: providing aprocess chamber having a wall; providing a plasma source adjacent to thewall of the process chamber; providing a work piece support within theprocess chamber, the work piece support having an electrostatic chuck;placing the substrate on a carrier support to form a work piece;providing an intermediate ring interposed between the substrate and theframe; loading the work piece onto the work piece support; generating aplasma through the plasma source; and etching the work piece through thegenerated plasma.

Another object of the present invention is to provide a method forplasma dicing a substrate, the method comprising: assembling a workpiece having a rigid frame, an intermediate ring, a flexible membrane,and at least one substrate; transferring said work piece into aprocessing chamber; exposing the substrate of said work piece to aplasma; modifying said work piece by removing the rigid frame; andprocessing said modified work piece.

The foregoing has outlined some of the pertinent objects of the presentinvention. These objects should be construed to be merely illustrativeof some of the more prominent features and applications of the intendedinvention. Many other beneficial results can be attained by applying thedisclosed invention in a different manner or modifying the inventionwithin the scope of the disclosure. Accordingly, other objects and afuller understanding of the invention may be had by referring to thesummary of the invention and the detailed description of the preferredembodiment in addition to the scope of the invention defined by theclaims taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The present invention describes a plasma processing apparatus whichallows for plasma dicing of a semiconductor substrate. After devicefabrication and wafer thinning, the front side (circuit side) of thesubstrate is masked using conventional masking techniques which protectsthe circuit components and leaves unprotected areas between the die. Thesubstrate is mounted on a thin tape which is supported within a rigidframe. The substrate/tape/frame assembly is transferred into a vacuumprocessing chamber and exposed to reactive gas plasma where theunprotected areas between the die are etched away. During this process,the frame and tape are protected from damage by the reactive gas plasma.The processing leaves the die completely separated. After etching, thesubstrate/tape/frame assembly is additionally exposed to plasma whichremoves potentially damaging residues from the substrate surface. Aftertransfer of the substrate/tape/frame assembly out of the processchamber, the die are removed from the tape using well known techniquesand are then further processed (e.g., packaged) as necessary.

Another feature of the present invention is to provide a method forplasma dicing a substrate. The substrate can have a semiconducting layersuch as Silicon and/or the substrate can have a III-V layer such asGaAs. The substrate can have a protective layer such as a photoresistlayer that is patterned on a circuit side of the substrate. A processchamber having a wall with a plasma source adjacent to the wall of theprocess chamber is provided. The plasma source can be a high densityplasma source. A vacuum pump in fluid communication with the processchamber and a gas inlet in fluid communication with the process chambercan be provided. A work piece support within the process chamber isprovided. A work piece is formed by placing the substrate on a carriersupport. The work piece can be formed by adhering the substrate to asupport film and then mounting the substrate with the support film to aframe. The support film can have an upper surface and a lower surface.The support film can have a polymer layer and/or a conductive layer. Thesupport film can be standard dicing tape. The frame can have aconductive layer and/or a metal layer. The work piece is then loadedonto the work piece support for plasma processing. An RF power sourcecan be coupled to the work piece support to create a plasma around thework piece. A thermal communication between the work piece and the workpiece support can be provided by supplying a pressurized gas such ashelium from the work piece support to the work piece. An electrostaticchuck can be incorporated into the work piece support whereby theelectrostatic chuck can clamp the support film to the electrostaticchuck. An intermediate ring is interposed between the substrate and theframe. The intermediate ring can contact the support film. Theintermediate ring can further comprise an inner diameter and thesubstrate can further comprise an outer diameter wherein the innerdiameter of the intermediate ring is greater in size than the outerdiameter of the substrate. The intermediate ring can be positionedcoplanar with the substrate. The intermediate ring can comprise one ormore pieces. The intermediate ring can be positioned on the uppersurface of the support film and the substrate can be positioned on theupper surface of the support film. The pressure within the processchamber can be reduced through the vacuum pump and a process gas can beintroduced into the process chamber through the gas inlet. A plasma isgenerated through the plasma source whereby the work piece is processedby the generated plasma. A vacuum compatible transfer module can beprovided that communicates with the process chamber. The work piece canbe loaded onto a transfer arm in the vacuum compatible transfer modulewhereby the process chamber is maintained under vacuum during a transferof the work piece from the vacuum compatible transfer module to theprocess chamber.

Yet another feature of the present invention is to provide a method forplasma dicing a substrate. The substrate can have a semiconducting layersuch as Silicon and/or the substrate can have a III-V layer such asGaAs. The substrate can have a protective layer such as a photoresistlayer that is patterned on a circuit side of the substrate. A processchamber having a wall with a plasma source adjacent to the wall of theprocess chamber is provided. The plasma source can be a high densityplasma source. A vacuum pump in fluid communication with the processchamber and a gas inlet in fluid communication with the process chambercan be provided. A work piece support within the process chamber isprovided. A work piece is formed by placing the substrate on a carriersupport. The work piece can be formed by adhering the substrate to asupport film and then mounting the substrate with the support film to aframe. The support film can have an upper surface and a lower surface.The support film can have a polymer layer and/or a conductive layer. Thesupport film can be standard dicing tape. The frame can have aconductive layer and/or a metal layer. The work piece is then loadedonto the work piece support for plasma processing. An RF power sourcecan be coupled to the work piece support to create a plasma around thework piece. A thermal communication between the work piece and the workpiece support can be provided by supplying a pressurized gas such ashelium from the work piece support to the work piece. An electrostaticchuck can be incorporated into the work piece support whereby theelectrostatic chuck can clamp the support film to the electrostaticchuck. A cover ring can be interposed between the plasma source and thework piece. An intermediate ring is interposed between the substrate andthe frame. The intermediate ring may not overlap the cover ring. Theintermediate ring can further comprise an inner diameter and thesubstrate can further comprise an outer diameter wherein the innerdiameter of the intermediate ring is greater in size than the outerdiameter of the substrate. The intermediate ring can be positionedcoplanar with the substrate. The intermediate ring can comprise one ormore pieces. The intermediate ring can be positioned on the uppersurface of the support film and the substrate can be positioned on theupper surface of the support film. The pressure within the processchamber can be reduced through the vacuum pump and a process gas can beintroduced into the process chamber through the gas inlet. A plasma isgenerated through the plasma source whereby the work piece is processedby the generated plasma. A vacuum compatible transfer module can beprovided that communicates with the process chamber. The work piece canbe loaded onto a transfer arm in the vacuum compatible transfer modulewhereby the process chamber is maintained under vacuum during a transferof the work piece from the vacuum compatible transfer module to theprocess chamber.

Still yet another feature of the present invention is to provide amethod for plasma dicing a substrate. The substrate can have asemiconducting layer such as Silicon and/or the substrate can have aIII-V layer such as GaAs. The substrate can have a protective layer suchas a photoresist layer that is patterned on a circuit side of thesubstrate. A process chamber having a wall with a plasma source adjacentto the wall of the process chamber is provided. The plasma source can bea high density plasma source. A vacuum pump in fluid communication withthe process chamber and a gas inlet in fluid communication with theprocess chamber can be provided. A work piece support within the processchamber is provided. A work piece is formed by placing the substrate ona carrier support. The work piece can be formed by adhering thesubstrate to a support film and then mounting the substrate with thesupport film to a frame. The support film can have an upper surface anda lower surface. The support film can have a polymer layer and/or aconductive layer. The support film can be standard dicing tape. Theframe can have a conductive layer and/or a metal layer. The work pieceis then loaded onto the work piece support for plasma processing. An RFpower source can be coupled to the work piece support to create a plasmaaround the work piece. A thermal communication between the work pieceand the work piece support can be provided by supplying a pressurizedgas such as helium from the work piece support to the work piece. Anelectrostatic chuck is incorporated into the work piece support wherebythe electrostatic chuck can clamp the support film to the electrostaticchuck. The electrostatic chuck can have at least one clamping electrode.An intermediate ring is interposed between the substrate and the frame.The intermediate ring may overlap the clamping electrode of theelectrostatic chuck. The intermediate ring can completely overlap theclamping electrode of the electrostatic chuck. The intermediate ring canfurther comprise an inner diameter and the substrate can furthercomprise an outer diameter wherein the inner diameter of theintermediate ring is greater in size than the outer diameter of thesubstrate. The intermediate ring can be positioned coplanar with thesubstrate. The intermediate ring can comprise one or more pieces. Theintermediate ring can be positioned on the upper surface of the supportfilm and the substrate can be positioned on the upper surface of thesupport film. The pressure within the process chamber can be reducedthrough the vacuum pump and a process gas can be introduced into theprocess chamber through the gas inlet. A plasma is generated through theplasma source whereby the work piece is processed by the generatedplasma. A vacuum compatible transfer module can be provided thatcommunicates with the process chamber. The work piece can be loaded ontoa transfer arm in the vacuum compatible transfer module whereby theprocess chamber is maintained under vacuum during a transfer of the workpiece from the vacuum compatible transfer module to the process chamber.

Another feature of the present invention is to provide a method forplasma dicing a substrate. A work piece is assembled using a rigidframe, an intermediate ring, a flexible membrane, and at least onesubstrate. The substrate can have a semiconducting layer such as Siliconand/or the substrate can have a III-V layer such as GaAs. The substratecan have a protective layer such as a photoresist layer that ispatterned on a circuit side of the substrate. The flexible membrane canhave a polymer layer and/or a conductive layer. The flexible membranecan be standard dicing tape. The frame can have a conductive layerand/or a metal layer. The intermediate ring can be positioned coplanarwith the substrate. The intermediate ring can comprise one or morepieces. The intermediate ring can be positioned on the upper surface ofthe support film and the substrate can be positioned on the uppersurface of the support film. The work piece is then transferred into aprocessing chamber. The substrate of the work piece is exposed to aplasma. After plasma processing, the work piece is modified by removingthe rigid frame. Then, the modified work piece is sent for downstreamprocessing.

The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription of the invention that follows may be better understood sothat the present contribution to the art can be more fully appreciated.Additional features of the invention will be described hereinafter whichform the subject of the claims of the invention. It should beappreciated by those skilled in the art that the conception and thespecific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top down view of a semiconductor substrate illustratingindividual devices separated by streets;

FIG. 2 is a cross-sectional view of a semiconductor substrateillustrating individual devices separated by streets;

FIG. 3 is a cross-sectional view of a semiconductor substrate mounted totape and a frame;

FIG. 4 is a cross-sectional view of a semiconductor substrate mounted totape and a frame being etched by a plasma process;

FIG. 5 is a cross-sectional view of separated semiconductor devicesmounted to tape and a frame;

FIG. 6 is a cross-sectional view of a vacuum processing chamber;

FIG. 7 is a cross-sectional of a wafer/frame in process position;

FIG. 8 is an enlarged cross-sectional view of a frame and a cover ringin a vacuum processing chamber;

FIG. 9 is a cross-sectional view of a section of the inside the chamberwith the cover ring mounted to a chamber wall;

FIG. 10 is a cross-sectional view of a section of the inside the chamberwith the cover ring mounted to an internal heat sink;

FIG. 11 is a top down view of a semiconductor substrate mounted to tapeand a frame supported by a transfer arm;

FIG. 12 is a cross-sectional view of a semiconductor substrate mountedto tape and a frame supported by a transfer arm;

FIG. 13 is a cross-sectional view of a wafer/frame in a transferposition;

FIG. 14 is a top view of a screen;

FIG. 15 is a top view of an electrostatic chuck according to the priorart;

FIG. 16 is a top view of a multi-zone electrostatic chuck according tothe prior art;

FIG. 17 is a top view of an electrostatic chuck according to oneembodiment of the present invention;

FIG. 18 is a cross-sectional view of a substrate on an electrostaticchuck according to the prior art;

FIG. 19 is a cross-sectional view of a work piece on an electrostaticchuck according to one embodiment of the present invention;

FIG. 20 is a cross-sectional view of an electrostatic chuck according toone embodiment of the present invention;

FIG. 21 is a cross-sectional view of an electrostatic chuck according toone embodiment of the present invention;

FIG. 22 is a top view of a work piece with multiple substrates accordingto one embodiment of the present invention;

FIGS. 23 a-23 c are cross sectional views of variations of mechanicalpartitions according to the present invention;

FIG. 24 is a cross sectional view of etched features according to oneembodiment of the present invention;

FIG. 25 is a flow chart of a method to adjust a mechanical partitionaccording to the present invention;

FIG. 26 is a cross section of an electrostatic chuck according to oneembodiment of the present invention;

FIG. 27 is a cross section of an electrostatic chuck according to oneembodiment of the present invention;

FIG. 28 is a top down view of a cover ring according to the presentinvention;

FIG. 29 is a cross section of a cover ring and ESC according to thepresent invention;

FIG. 30 is a cross section of a cover ring and ESC according to thepresent invention;

FIG. 31 a is a top view of a group of individual devices according tothe prior art;

FIG. 31 b is a top view of a group of individual devices and a processcontrol monitor according to the prior art;

FIG. 32 is a top view of a group of individual devices according to thepresent invention;

FIG. 33 is a top view of a group of individual devices and a processcontrol monitor according to the present invention;

FIG. 34 is a top view of a group of individual devices and a processcontrol monitor according to the present invention;

FIG. 35 is a top view of a group of individual devices and processcontrol monitors according to the present invention;

FIG. 36 is a top down view of a semiconductor substrate illustratingindividual devices separated by streets according to the prior art;

FIG. 37 is a top down view of a semiconductor substrate illustratingindividual devices separated by streets according to the presentinvention;

FIG. 38 is a top down view of a cover ring according to the presentinvention;

FIG. 39 is a top down view of a cover ring according to the presentinvention;

FIG. 40 is a top down view of a cover ring according to the presentinvention;

FIG. 41 is a top down view of a cover ring according to the presentinvention;

FIG. 42 is a cross-sectional view of a semiconductor substrate mountedto tape and a frame containing an intermediate ring according to oneembodiment of the present invention;

FIG. 43 is a cross-sectional view of a section of the inside the chamberwith the cover ring and the work piece containing an intermediate ringaccording to one embodiment of the present invention;

FIG. 44 is a cross-sectional view of a work piece containing anintermediate ring on an electrostatic chuck according to one embodimentof the present invention; and

FIG. 45 is a flow chart of a method to process a work piece containingan intermediate ring according to one embodiment of the presentinvention.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

A typical semiconductor substrate after device fabrication isillustrated in FIG. 1. The substrate (100) has on its surface a numberof areas containing device structures (110) separated by street areas(120) which allows for separation of the device structures intoindividual die. Although silicon is commonly used as a substratematerial, other materials chosen for their particular characteristicsare frequently employed. Such substrate materials include GalliumArsenide and other III-V materials or non-semi-conductor substrates onwhich a semi-conducting layer has been deposited. Further substratetypes may also include Silicon-On-Insulator (SOI) wafers andsemiconductor wafers mounted on carriers. While the example abovedescribes die separated by streets, aspects of the invention may bebeneficially applied to other pattern configurations on a substrate.

In the present invention, as is shown in a cross sectional view in FIG.2, the device structures (110) are then covered with a protectivematerial (200) while the street areas (120) remain unprotected. Thisprotective material (200) can be a photoresist, applied and patterned bywell-known techniques. Some devices, as a final process step are coatedwith a protective dielectric layer such as silicon dioxide or PSG whichis applied across the whole substrate. This can be selectively removedfrom the street areas (120) by patterning with photoresist and etchingthe dielectric material, as is well known in the industry. This leavesthe device structures (110) protected by the dielectric material and thesubstrate (100) substantially unprotected in the street areas (120).Note that in some cases test features to check the wafer quality may belocated in the street areas (120). Depending on the specific waferfabrication process flow, these test features may or may not beprotected during the wafer dicing process. Although the device patternillustrated shows oblong die, this is not necessary, and the individualdevice structures (110) may be any other shape, such as hexagons, asbest suits the optimum utilization of the substrate (100). It isimportant to note that while the previous example considers dielectricmaterials as the protective film, that the invention may be practicedwith a wide range of protective films including semi-conductive andconductive protective films. Furthermore, the protective layer canconsist of multiple materials. It is also important to note that someportion of the protective film may be an integral part of the finaldevice structure. (e.g., a passivation dielectric, metal bonding pad,etc.). Furthermore, the present invention can also be beneficially usedwith bulk wafers without the necessity of having devices or devicestructures. One such example may be a semiconductor substrate (Silicon,III-V compounds, etc.), mounted on a carrier or not mounted, covered bya masking material defining the structures to be etched. The substratemay also contain at least one additional layer with different materialproperties, such as for example an insulating layer.

The substrate (100) may be thinned, typically by a grinding process,which reduces the substrate thickness to a few hundred microns to asthin as approximately 30 microns or less. As is shown in FIG. 3, thethinned substrate (100) is then adhered to a tape (300) which in turn ismounted in a rigid frame (310) to form a work piece (320). The tape(300) can be a UV release tape (e.g. UV release dicing tape) as is knownin the art. The frame is typically metal or plastic, though other framematerials are possible. The frame (310) can be any shape, including anassymetric shape. The tape (300) is typically made from acarbon-containing polymer material, and may additionally have a thinconductive layer applied to its surface. The tape (300) provides supportfor the thinned substrate (100) which is otherwise too fragile to handlewithout breakage. It should be noted that the sequence of patterning,thinning and then mounting is not critical and the steps may be adjustedto best fit the particular devices and substrate and the processingequipment used. It is important to note that while the previous exampleconsiders a work piece (320) that is comprised of mounting a substrate(100) on an adhesive tape (300) which in turn is attached to a frame(310), that the invention is not limited by the configuration of thewafer and carrier. The wafer carrier can be comprised a variety ofmaterials. The carrier supports the substrate during the plasma dicingprocess. Furthermore, the wafer need not be attached to the carrierusing an adhesive—any method that holds the wafer to the carrier andallows a means thermal communication of the substrate to the cathode issufficient (e.g., an electrostatically clamped carrier, a carrier with amechanical clamping mechanism, etc.).

After mounting the substrate (100) with the tape (300) in the dicingframe (310), the work piece (320) is transferred into a vacuumprocessing chamber. Ideally, the transfer module is also under vacuumwhich allows the process chamber to remain at vacuum during transfer,reducing processing time and preventing exposure of the process chamberto atmosphere and possible contamination. As shown in FIG. 6, the vacuumprocessing chamber (600) is equipped with a gas inlet (610), a highdensity plasma source (620) to generate a high density plasma, such asan Inductively Coupled Plasma (ICP). An ICP source typically consists ofan antenna (624) in proximity to a dielectric wall (622). RF energy iscoupled from the antenna (624) through the dielectric wall (622) intothe vacuum processing chamber to form a plasma (697). The high densityplasma source (620) is typically energized by an RF power source (637)through an impedance matching network (642). The high density plasmasource typically operates between approximately 100 W up to 10's of kWof RF power. The RF power source (637) typically operates at frequenciesbetween 1 kHz to 200 MHz. An ICP plasma source may contain more than oneantenna as is known in the art. The vacuum processing chamber (600) alsocontains a work piece support (630) to support the work piece (320), anRF bias power source (640) to couple RF power to the work piece (320)through the work piece support (630) and a vacuum pump (650) for pumpinggas from the processing chamber (600). The RF bias power source (640)can be coupled through an impedance matching network (641) to moreefficiently couple the RF energy to the workpiece support (630). Duringprocessing, the unprotected areas (120) of substrate (100) are etchedaway using a reactive plasma etch process (400) as shown in FIG. 4. Thisleaves the devices (110) separated into individual die (500) as shown inFIG. 5. In another embodiment of the invention, the unprotected areas(120) of the substrate (100) are partially etched away using a reactiveplasma etch process (400). In this case, a downstream operation, such asa mechanical breaking operation, can be used to complete the dieseparation. These downstream methods are well known in the art.

While the previous example describes the invention using a vacuumchamber in conjunction with a high density plasma (e.g., ECRs, ICP,helicon, and magnetically enhanced plasma sources), it is also possibleto etch the unprotected areas of the substrate using a wide range ofplasma processes. For example, one skilled in the art can imaginevariations of the invention using a low density plasma source in avacuum chamber or even the use of plasmas at or near atmosphericpressures.

When the work piece (substrate/tape/frame assembly) (320) is in theposition for plasma processing, the frame (310) can be protected fromexposure to the plasma (400). Exposure to the plasma (400) may causeheating of the frame (310) which in turn may cause local heating of themounting tape (300). At temperatures above approximately 100° C., thephysical properties of the tape (300) and its adhesive capability maydeteriorate and it will no longer adhere to the frame (310).Additionally, exposure of the frame (310) to the reactive plasma gas maycause degradation of the frame (310). Since the frame (310) is typicallyre-used after wafer dicing, this may limit the useful lifetime of aframe (310). Exposure of the frame (310) to the plasma (400) may alsoadversely affect the etch process: for example the frame material mayreact with the process gas, effectively reducing its concentration inthe plasma which may reduce the etch rate of the substrate material,thus increasing process time. To protect the frame (310), a protectivecover ring (660), as shown in FIGS. 6, 7 and 8, is positioned above theframe (310). In one embodiment, the cover ring (660) does not touch theframe (310) since contact with the frame (310) (which would occur duringtransfer into the process chamber (600)) may generate undesirableparticles.

In FIG. 8, dimension (800) represents the distance between the coverring (660) and the frame (310). This dimension can range from greaterthan approximately 0.1 mm to less than approximately 20 mm with anoptimal value of 4 mm. If the distance (800) is too large, plasma willcontact the frame (310) and the benefits of the cover ring (660) may belost.

In one embodiment the cover ring (660) is temperature controlled.Without cooling, the cover ring (660) temperature may increase due toexposure to the plasma and in turn heat the tape (300) and the frame(310) via thermal radiation, causing degradation as noted above. For thecase where the cover ring (660) is cooled, cooling of the cover ring(660) is accomplished by having it in direct contact with a cooled body,such as the wall of the process chamber (600) shown in FIG. 9 or a heatsink (1000) located within the process chamber (600) shown in FIG. 10.To ensure that heat is adequately removed from the cover ring (660) tothe heat sink (1000), the cover ring (660) should be made of a materialthat has good thermal conductivity. Such materials include many metals,for example Aluminum, but other thermally conductive materials, such asAluminum Nitride and other ceramics can be used. The choice of the coverring material is chosen to be compatible with the plasma process gasesused. While Aluminum is satisfactory for Fluorine based processes, analternate material, such as Aluminum Nitride, or the addition of aprotective coating, such as Aluminum Oxide may be necessary whenChlorine based processes are used. Operation temperature of the coverring (660) during plasma processing ranges from about 25° C. to about350° C. Preferably the temperature of the cover ring (660) is held inthe range of 50° C. to 90° C. which minimizes thermal radiation to thetape (300) and the frame (310) and ensures that the tape (300) maintainsits mechanical integrity. Alternatively, the cover ring (660) may betemperature controlled by bringing the cover ring (660) into contactwith a temperature controlled fluid. This fluid can be a liquid or gas.In the case where the cover ring (660) temperature is controlled by afluid, the cover ring (660) may contain a number of fluid channels tofacilitate heat transfer. These fluid channels can be internal to thecover ring (660), externally attached, or some combination of the two.

In one embodiment, the cover ring (660) can extend from the substratediameter to the inner chamber diameter continuously. To avoid a loss inpumping conductance, which can adversely affect pressure control withinthe process chamber (600), a plurality of pumping holes (1010) can beadded to the cover ring (660) which allows sufficient conductance of theprocess gas while still providing a path for heat removal from the coverring (660). In FIGS. 9 and 10, a plurality of holes (1010) arranged in aspecific geometry is shown, but the shape, density, size, pattern andsymmetry of the holes (1010) can vary depending on the process chamber(600) dimensions and the pumping conductance required. It is preferredthat the holes (1010) do not overlap the tape (300). In anotherembodiment, the holes (1010) do not overlap the work piece (320).

The work piece (substrate/tape/frame assembly) (320) is transferred bothinto and out of the process chamber (600) by a transfer arm (1100) thatsupports the frame (310) and substrate (100) so that they are maintainednearly coplanar as shown in FIGS. 11 and 12. The transfer arm (1100) maysupport both the tape (300) and the frame (310) or the frame (310)alone, but it is important that the assembly (320) not be supportedbeneath the substrate (100) area alone because of the fragile nature ofthinned substrates (100). The transfer arm (1100) has an alignmentfixture (1110) attached to it that aligns the frame (310) in arepeatable position before being transferred into the process chamber(600). The frame (310) can also be aligned by other techniqueswell-known in semiconductor processing (e.g., optical alignment). Thealignment can also be performed on the substrate (100) by suchwell-known techniques. It is important that the work piece(substrate/tape/frame assembly) (320) be aligned before placement withinthe process chamber (600) to avoid miss-processing as explained below.

In FIG. 8, the substrate-to-frame dimension (810) represents thedistance between the outer diameter of the substrate (100) and the innerdiameter of the frame (310). This may be 20 mm to 30 mm (e.g., DiscoCorporation dicing frame has an inner diameter of about 250 mm for 200mm substrates, so that the substrate-to-frame dimension (810) isnominally 25 mm). During mounting of the wafer (100) on the tape (300)within the frame (310), the deviation of wafer (100) placement may be asmuch as 2 mm so that the cover ring to substrate distance (820), whichis the distance between the substrate (100) outer diameter and the innerdiameter of the cover ring (660) can also vary from assembly to assemblyby up to 2 mm. If at some point the cover ring to substrate distance(820) is less than zero, the cover ring (660) will overlay the edge ofthe substrate (100). This area of the substrate will be shadowed andprevented from etching, which can prevent die separation and causeproblems in subsequent processing steps. It is preferred that the coverring (660) does not overlap the substrate (100). Alignment of thesubstrate/tape/frame assembly (320) prior to transfer is required toprevent such problems. Further, to additionally ensure that cover ringto substrate distance (820) is not less than zero, the cover ring innerdiameter should be greater than the diameter of the substrate (100). Itis preferred that the cover ring inner diameter be 5 mm greater than thesubstrate diameter (e.g., 205 mm cover ring inner diameter for 200 mmsubstrate). The cover ring overhang dimension (830) in FIG. 8 representsthe distance from the inner diameter of the cover ring (660) to theinner diameter of the frame (310). Alignment of the frame (310) prior totransfer into the process chamber (600) ensures that the cover ringoverhang dimension (830) remains essentially constant for the entirecircumference around the substrate (100) and that any portion of tape(300) that is not contacted by the Electrostatic chuck (ESC) (670) issubstantially shadowed from the plasma. In a preferred embodiment anytape (300) that is not in thermal contact with the ESC (670) isoverlapped by the cover ring (660). In one embodiment, the cover ring(660) and substrate (100) are located in different planes. Therefore theinner periphery of the cover ring (661) is not adjacent to the outerperiphery (101) of the substrate.

When the work piece (e.g., substrate/tape/frame assembly) (320) istransferred into the process chamber (600), it is placed onto thelifting mechanism (680) and removed from the transfer arm (1100). Thereverse process occurs during transfer of the work piece (e.g.,substrate/tape/frame assembly) (320) out of the process chamber (600).The lifting mechanism (680) touches the frame (310) area and provides nopoint contact to the substrate (100). Point contact to the substrate(100) can cause damage to the substrate (100), particularly after dieseparation and unloading of the work piece (320), since the flexibilityof the tape (300) may cause the die to contact each other and damage tooccur. FIG. 13 shows the lifting mechanism (680) lifting the frame (310)from the underside; however, the frame (310) can also be removed fromthe transfer arm (1100) by contact with the top surface, bottom surface,outer diameter of the frame (310) or any combination of these using aclamping device. In order to have enough clearance to place the workpiece (320) on the work piece support (630) to process the substrate(100), the frame (310), the work piece support (630), and the cover ring(660) can move relative to each other. This can be accomplished bymoving the cover ring (660), the work piece support (630), or thelifting mechanism (680) or any combination of the three.

During plasma processing, heat is transferred to all of the surfaces theplasma touches including the substrate (100), tape (300), and frame(310). The cover ring (660) will minimize the heat transfer to areas ofthe tape (300) and the frame (310), but the substrate (100) must beexposed to the plasma (400) for processing.

As shown in FIG. 6, a perforated mechanical partition (690) may beinterposed between the plasma source (620) and the work piece support(630). The mechanical partition (690) can be electrically conductive(e.g., made from metal or metal coated). The mechanical partition (690)is preferably made of Aluminum. The mechanical partition (690) can helpreduce the ion density as well as the plasma emission intensity reachingthe work piece, while allowing a high level of neutral species to reachthe work piece. The present invention offers control over the iondensity and plasma emission intensity reaching the work piece. It ispreferred for applications relevant to this invention, that the iondensity and plasma emission intensity from the plasma source (620)reaching the work piece be attenuated in the range of 10% to 50% by themechanical partition. In one preferred embodiment, the attenuation bythe mechanical partition can be greater than 10%. In one preferredembodiment, the attenuation by the mechanical partition can be greaterthan 30%. In yet another preferred embodiment, the attenuation by themechanical partition can be greater than 50%.

In one embodiment, the plasma below the mechanical partition (690) issustained by the application of RF bias power by an RF power supply(640) through the work piece support (630) and/or ESC (670). In thiscase, the plasma that acts upon the substrate (100) is sustained by theRF bias power through the work piece support (630) and/or ESC (670).

In the present invention, the temperature of the mechanical partition(690) can range between 0° C. and 350° C. It is preferable to maintainthe mechanical partition (690) at a temperature greater than 60° C. Themechanical partition can fully or partially separate the work piece fromthe plasma source. It is preferable that the partition overlaps thesubstrate to be etched. In a preferred embodiment, the substrate (100)is completely overlapped by the mechanical partition (690). In yetanother embodiment, the diameter of the mechanical partition (690) is atleast 10% larger than the diameter of the substrate (100).

The mechanical partition (690) should be positioned between thesubstrate (100) and the plasma source (620). The mechanical partition(690) can completely segregate the area in the plasma source (620) fromthe rest of the chamber (600). In order to prevent the pattern ofperforations in the mechanical partition (690) from printing on thesubstrate (100) it is preferred that the distance from the top of thesubstrate to the bottom surface of overlapping mechanical partition(690) be at least as large as the plasma sheath at the substrate (100)top surface. The thickness of the plasma sheath is a function ofpressure, gas composition and plasma density among other parameters.Typically, plasma sheath thicknesses range from approximately 100microns to approximately 2 centimeters. In one embodiment, themechanical partition (690) is at least 0.1 mm from the top surface ofthe substrate (100). Preferably the mechanical partition (690) is atleast 1 cm from the top surface of the substrate (100).

The perforations (695) in the mechanical partition (690) allow theplasma to diffuse through and act upon the substrate. The perforations(695) may be of any shape and dimensions (e.g., circular, hexagonal,ovals, any polygonal shapes, etc.). The mechanical partition thickness(2620) can be designed to affect the plasma species composition thatacts upon the surface of the substrate. As shown in FIG. 23 c, thethickness (2620) of the mechanical partition (690) can vary across thepartition. The thickness variation can be continuous, discrete, or acombination of both. Preferably, the mechanical partition thickness(2620) is less than approximately 2.5 cm. The perforation hole diameters(2600) can range from approximately 0.1 mm up to approximately 1 cm.Typical aspect ratios of the perforations (695) can be between 0.5:1 upto 100:1, but preferably between 0.5:1 to 10:1. In one embodiment, themechanical partition (690) reduces the plasma ion density from greaterthan approximately 10¹¹ cm⁻³ within the plasma source to less thanapproximately 10¹⁰ cm⁻³ near the substrate surface.

The perforations (695) in the mechanical partition (690) can be arrangedin a number of ways. FIG. 14 shows a top view of a mechanical partition(690) with a pattern of perforations (695) that are uniformlydistributed in a rectilinear pattern. While FIG. 14 shows a rectilinearpattern of perforations (695), alternate configurations includinghexagonal, honeycomb or circular perforation patterns may be used. Thedimensions of the perforations (2600) may vary across the mechanicalpartition (690) (e.g., FIGS. 23 b and 23 c).

In an alternate embodiment, the perforation pattern in the mechanicalpartition (690) may designed such that the spacing between perforations(2610) is variable (e.g., FIGS. 23 b and 23 c). In yet anotherembodiment, the size and/or shape of the perforations may vary acrossthe mechanical partition (690). The mechanical partition (690) can havea perforation pattern such that both the perforation size (2600) andspacing (2610) vary across the partition.

While the schematic in FIG. 6 shows a process chamber (600) with onemechanical partition (690), it may be beneficial to have more than onemechanical partition (690) disposed between the plasma source (620) andthe substrate (100). The mechanical partitions (690) can be the samesize and shape, or can be different sizes and/or shapes. The multiplemechanical partitions (690) may be configured in the same plane ordifferent planes (e.g., overlapped or stacked partitions). The multiplemechanical partitions (690) may have perforation shapes, sizes andpatterns that are identical or different from one another.

High density plasma sources (620) can generate high levels of UVradiation. This UV radiation may cause undesirable side reactions ordamage the substrate (100). In some applications it is desirable toshield the substrate from UV emissions from the plasma source (620). Oneway to reduce this emission is to limit the direct path of UV emissionfrom the plasma source to the substrate (e.g., limit the “line of sight”from the plasma source to the substrate). In the case of partitions thatare in different planes and overlapped, it may be beneficial to ensurethat the perforations (695) in the overlapped region of the partitionsdo not coincide (e.g., the partitions have some region of overlap, wherethe perforations of the partitions do not overlap one another). In oneembodiment of the overlapped partitions (695), at least one perforation(695) in an overlapped region of a partition does not overlap aperforation in another partition. In yet another embodiment ofoverlapped partitions, none of the perforations in the partitions (695)overlap one another. In this configuration there is no direct path forlight emitted from the plasma source to reach the substrate through theoverlapped region of the partitions.

The pattern of perforations (695) in the mechanical partition (690) maybe used to adjust the etch uniformity on the substrate (100). Thisadjustment may be accomplished through varying the thickness of thepartition (2620), the perforation size (2600), perforation shape,perforation spacing (2610) or any combination of these factors.

In order to determine the correct perforation (695) configuration for amechanical partition (690), the following steps may be followed for agiven partition configuration (see FIG. 25): process a substrate,measure at least one wafer property (e.g., material etch rate,selectivity ratio, feature profile, etc.), adjust the mechanicalpartition (690) (e.g., partition spacing, distance from partition tosubstrate, partition thickness and/or perforation size, spacing, shape,and/or aspect ratio, etc.) based on at least one measured property.Another wafer is processed, and if necessary the mechanical partition(690) is iterated to achieve the desired wafer property or properties.

Typically, in a chemically driven plasma etch process, it is desirableto maximize the ratio of the substrate etch rate to the masking materialetch rate (etch selectivity) while maintaining a desired featureprofile. In the case of silicon etching using a time divisionmultiplexed process (e.g., Bosch process or DRIE), this is accomplishedby applying some minimum RF bias power to the substrate through thesubstrate support in order to maintain a desired feature profile.Typically, this RF bias power is less than approximately 50 W. At higherRF bias powers, the etch selectivity (material etch rate/mask etch rate)can be undesirably reduced. When a mechanical partition is placedbetween the high density plasma source and the substrate, the density ofions available to etch the substrate is significantly reduced. Thisallows higher RF bias powers to be beneficially applied to the substratein comparison to the prior art. With the mechanical partition betweenthe plasma source and the substrate, beneficial time divisionmultiplexed (e.g., Bosch, DRIE) process results can be achieved at RFbias powers applied to the substrate in a range of 50 W to 150 W. In apreferred embodiment, the RF bias power applied to the substrate isgreater than approximately 50 W. In another preferred embodiment, the RFbias power applied to the substrate is greater than approximately 100 W.In another preferred embodiment, the RF bias power applied to thesubstrate is greater than approximately 150 W.

During plasma processing, additional cooling of the substrate (100) isoften provided through the use of an Electrostatic chuck (ESC) (670).FIGS. 15-17 show examples of ESCs (670) that are commonly used insemiconductor processing to apply an attractive force to a substrate(100) while a pressurized fluid; typically a gas, such as Helium ismaintained in the gap (2000) between the substrate (100) and the ESC.This ensures that efficient heat transfer can occur between thesubstrate (100) and the work piece support (630), which can betemperature controlled. Note in FIGS. 15 and 16, for illustrationpurposes, that the dashed line represents the area of the ESC that thewafer (100) overlaps. During processing the wafer (100) sits on the topsurface of the ESC (670).

FIG. 15 shows a top view of an electrostatic chuck as is known in theart. An ESC (670) will commonly have a sealing region or regions (1700)to confine the pressurized fluid between the ESC and the substrate (100)being clamped. The sealing regions (1700) are commonly employed near theperimeter of the ESC and around any features that would otherwise causethe pressurized fluid to leak and degrade the heat transfer. Some ESCsmake use of multiple concentric seal bands (1700) as shown in FIG. 16 togenerate discrete volumes or zones (1800, 1810) that allow independentcontrol of the fluid pressure within the respective zone. These ESCs arecommonly described as multi pressure zone ESCs. It is also possible thatthe pressure zones (1800, 1810) are not discrete and some of thepressurized fluid leaks between zones. Wide sealing regions (1700) aretypically not preferred. Typically, the thermal gradients across thework piece area which overlaps said wide sealing region may negativelyimpact some characteristic of the etch. On the contrary, if a sealingregion is not wide enough, the pressurized fluid may leak and heattransfer may degrade. As shown in FIG. 15, in the prior art the sealingregions or bands (1700) described above do not extend past the substrate(100) since doing so would expose the sealing surface of the seal band(1700) to potentially corrosive plasma gases that may decrease thelifetime of the ESC. FIG. 18 shows the cross sectional view of a rigidsubstrate (100) on an electrostatic chuck as is known in the art. Notethat the seal band (1700) is overlapped by the substrate (100).Furthermore, it is typical in the art to have the substrate (100) extendbeyond the edge of the sealing surface (1700) in order to accommodatefor any placement error during placement of the wafer on the ESC (670).It is also important to note that in the prior art that the lift pinholes (1720) and lift pins (2025) used to lift the substrate off the ESCare also located under the substrate (100)—inside or within theoutermost seal band (1700). Finally, ESCs known in the art have theclamping electrode(s) (2010) confined to the areas underneath thesubstrate (100). Therefore the clamping electrode (2010) is inside ofthe area defined by the outer seal band (1700)—both of which are insidethe wafer perimeter.

FIG. 19 shows a cross sectional view for one embodiment of the currentinvention. When clamping a flexible work piece (e.g., a work piece (320)containing tape (300), etc.), it is preferable to have at least oneclamping electrode (2010) overlap the sealing region (1700) as depictedin FIG. 19. This is particularly important when a flexible region of thework piece overlaps the sealing region (1700). Overlap of the clampingelectrode (2010) with the flexible work piece (300) helps minimizeHelium gas leakage. Preferably this overlap (2200) is greater than 1 mmwide. The overlap (2200) can include the inside edge of the seal bandperimeter, outer edge of the seal band perimeter, a region within theseal band, or some combination of the three.

In one embodiment of the invention, the region defined by the overlap ofthe clamping electrode (2010) and the sealing band (1700) form acontinuous boundary that circumscribes the substrate (100). In anotherembodiment of the invention, the seal band (1700) can be completelyoverlapped by the clamping electrode (2010).

In yet another embodiment of the invention, the clamping electrode(2010) may overlap the cover ring (660). The overlap (2240) is typicallyin the range of approximately 1 mm to less than approximately 10 mm. Inone preferred embodiment, the overlap (2240) is less than approximately1 mm. In another preferred embodiment, the overlap (2240) is less thanapproximately 10 mm. The overlap (2240) may be zero.

In another embodiment, some portion of the seal band (1700) is notoverlapped by the cover ring (660)—this unshielded seal band region(2250) is shown in FIG. 19. In this configuration, it is preferred thatthe clamping electrode (2010) overlaps some portion of the unshieldedseal band region (2250) (e.g., the seal band (1700) that is not coveredby the cover ring (660)). It is preferred that the overlap of theclamping electrode (2010) and the unshielded seal band region (2250) begreater than approximately 1 mm wide. It is also preferred that theoverlap of the clamping electrode (2010) and the unshielded seal bandregion (2250) circumscribe the substrate (100). In one embodiment, theclamping electrode (2010) overlaps the entire unshielded seal bandregion (2250) of the seal band (1700) that is not overlapped by thecover ring (660).

Said sealing region(s) (1700) are typically between 1 mm and 15 mm wide,but preferably less than 10 mm. With a work piece (substrate/tape/frameassembly) (320), the area outside the diameter of the substrate (100)and inside the inner diameter of the frame (310) is tape (300).

While the preceding examples are described for an ESC with a single zoneESC with one seal band, these embodiments can also be beneficiallyapplied to electrostatic chucks with multiple pressure zones (andmultiple seal bands).

Using a typical ESC, because the cover ring (660) is larger than thediameter of the substrate (100), there would be an area of tape (300)exposed to the plasma process that is not being clamped and temperaturecontrolled by the ESC (670) or being shielded from the plasma (400) bythe cover ring (660). Such an area of tape (300) would reach a hightemperature and possibly fail. Thus, FIG. 8 shows the use of an ESC(670) that is made purposely larger than the substrate diameter so thatany tape (300) which is exposed to the plasma in region (e.g., the areadefined by the cover ring to substrate distance (820)) is also clampedand temperature controlled. The ESC diameter can be extended outwards tothe outer perimeter of the frame (310), but the ESC diameter ispreferred to be at least 0.2 mm less than the inner diameter of theframe (310). For other frame form factors, the ESC diameter ispreferably smaller than the largest opening in the frame.

As shown in FIG. 15, typical ESCs as are known in the art and used insemiconductor processing have a pattern (1730) on their surface. Thepatterned surface (1730) is completely overlapped by the substrate (100)and is inside the seal band (1700). The helium inlet holes (1710) are inthe patterned area (1730). The pattern is typically tailored to controlcertain ESC characteristics such as; but not limited to, heat transfer,temperature uniformity, Helium gas diffusion, and clamping force. Thepattern can also be tailored to minimize particle generation. As shownin FIG. 18 the patterning generates at least one mostly planar surface(2020) that is below the substrate contact surface (2030) of the ESCthus forming at least one gap (2000) when a substrate is clamped. Thisgap (2000) is typically filled with a pressurized fluid such as Heliumto facilitate heat transfer.

FIG. 19 shows another embodiment of the invention. For an applicationlike plasma dicing, where the work piece contains a flexible membrane(300), it is preferable that the pattern spacing (2210) be chosen so asto minimize deformation of the membrane (300). For plasma dicing, thisis particularly important after the die (110) have been separated(singulated) and are only substantially supported by the flexible tape(300). When the pattern spacing (2210) is larger than at least onedimension (length and/or width, but not thickness) of an individual die,it is possible that die could tilt after being separated and contacteach other potentially causing damage to the die. In one embodiment, thepattern on the ESC surface has a pattern spacing (2210) less than thesmallest die dimension (length and/or width). The pattern depth has apreferred range of less than approximately 50 μm to less thanapproximately 100 μm. In a preferred embodiment, it is preferred thatthe pattern depth (2230) be less than 100 μm. In another preferredembodiment, it is preferred that the pattern depth (2230) be less than50 μm. The pattern depth (2230) may be less than 15 μm. Die sizes canrange from approximately tens of microns up to centimeters.

In another embodiment, the pattern feature size (2220) in the planeparallel to the sealing surface can be between 0.1 mm and 30 mm, butpreferably the pattern feature size (2220) is between 0.5 mm to 10 mm.The pattern spacing (2210) is typically at least the pattern featuresize (2220) in the plane parallel to the sealing surface, but preferablyat least 1.5 times said pattern feature size (2220). Although a size isused to describe the dimension of the pattern features, different shapesof similar dimensions can be used. The pattern features (2220) may varyin size and shape. Likewise, the pattern spacing (2210) between thepattern features (2220) may also vary in size, shape and depth.

In another embodiment, in order to prevent die from contacting oneanother once they are separated, the ESC region overlapping thesubstrate can be designed to have pattern features sizes (2220) andpattern feature spacings (2210) such that both the pattern feature size(2220) and pattern feature spacing (2210) are smaller than the die to besingulated. The substrate (100) can completely overlapped by thepatterned region of the ESC. Die sizes can range from approximately tensof microns up to several centimeters. In one embodiment the surface ofthe ESC (670) overlapped by the substrate (100) is roughened. Theroughening can be accomplished through physical (e.g., bead blasting,sand blasting, etc.) or chemical means or a combination of both. Theroughened surface allows the backside cooling gas (e.g., helium) to fillvoids between the ESC (670) and the work piece (320). It is preferredthat the roughness of the ESC surface underlying the work piece (320) isgreater than the roughness of the seal ring (1700). Seal ring areastypically have a surface roughness less than approximately 10micro-inches (R_(a)). It is further preferred that the roughness of theESC (670) surface that is overlapped by the substrate be greater thanapproximately 12 micro-inches (R_(a)). The roughness of the ESC (670)surface that is overlapped by the substrate can be greater thanapproximately 30 micro-inches (R_(a)). It is also preferred that theroughened ESC surface extends beyond the perimeter of the substrate(100) in a range of approximately 1 mm to approximately 10 mm. It isfurther preferred that the roughened surface extends at leastapproximately 1 mm beyond the perimeter of the substrate (100). Inanother preferred embodiment, the roughened surface of the ESC canextend more than approximately 10 mm from the perimeter of thesubstrate.

In the case where the work piece (320) contains more than one substrate(100) as shown in FIG. 22, it is preferred that the ESC (670) extendsbeyond the edge of at least one substrate (100)—preferably extendingbeyond the edges of all substrates (100). In order to confine thecooling gas (typically helium) behind the substrates, the tape (300)must form a sealing surface between the electrostatic chuck (670) andthe tape (300). This sealing surface is often called a seal band (1700).In one embodiment, the sealing surface (1700) is continuous and forms aregion that circumscribes all the substrates (100). In anotherembodiment, the sealing band (1700) may be discontinuous andcircumscribes at least one substrate. In yet another embodiment, eachsubstrate (100) is circumscribed by an individual seal band (1700). In afurther embodiment, the substrates (100) may overlay the sealing band(s)or alternatively, the sealing band(s) may lie outside the substrate(s)(100).

In the case where the work piece (320) contains multiple substrates, theESC (670) can contain a single clamping electrode (2010) (e.g.,monopolar) or multiple clamping electrodes (2010) (e.g., multipolar).When multiple substrates (100) are present on a work piece (320), it ispreferred that a clamping electrode (2010) extends beyond the perimeterof at least one substrate (100) on the work piece (320). Preferably, aclamping electrode extends beyond the perimeter of all substrates (100)on the work piece (320) in a preferred range of approximately 1 mm toapproximately 10 mm. It is preferred that a clamping electrode extendsat least 1 mm beyond each substrate (100) perimeter. In anotherembodiment, a clamping electrode (2010) can extend at least 10 mm beyondeach substrate (100) perimeter on the work piece (320). In anotherembodiment, a clamping electrode (2010) overlaps all of the substrates(100). In another embodiment, each substrate (100) is completelyoverlapped by a clamping electrode (2010). It is preferred that aclamping electrode (2010) is continuous (e.g., no cut-outs) where itoverlaps a substrate (100). It is also preferred that Helium inlet holes(1710) are not overlapped by any substrate (100). The Helium inlet holescan be at least 1 mm from any substrate perimeter.

In the prior art as shown in FIGS. 15 and 17, the areas of the ESC (670)that are not covered by the wafer (100) are covered and protected fromthe plasma by a filler ring (700). This is in contrast to the currentinvention where the top surface of the ESC (670) is protected fromplasma exposure by the tape (300). The filler ring (700) can beconfigured such that the filler ring (700) is not exposed to the plasma.In the case of multiple substrates (100) on a work piece (320), the topsurface is protected by the presence of the flexible tape (300) in thework piece (320). This is in contrast to prior art configurations thatprovide a protective cover over the ESC to protect the surface of theESC between the substrates from plasma exposure.

For all cases (single substrate or multiple substrates on a work piece(320)) where the ESC (670) contains more than one clamping electrode, itis preferred that the edge of any clamping electrode does not intersecta substrate (100). It is further preferred that the edge of a clampingelectrode is at least 1 mm away from the perimeter of a substrate (100).

When clamping a work piece where the surface in contact with the ESC isan electrical insulator, it is preferable that the electricalinsulator's relative static electric permittivity (commonly known as itsrelative dielectric constant) be greater than 2. It is also preferredthat the electrically insulating layer covering the ESC's clampingelectrode have a relative dielectric constant greater than 6, but cantypically be greater than 2. The relative dielectric constant of thepressurized fluid which fills the gap (2000) is preferably less than thelowest relative dielectric constant of any bounding electricalinsulators. The relative dielectric constant of the pressurized fluid isideally less than 2. The strong electric field within the gap leads to astrong clamping force exerted on the bottom surface of the work piece.The pressure of the fluid in the gap (2000) is typically between 1 Torrand 100 Torr, but preferably between 1 Torr and 40 Torr.

As shown in FIG. 18, it is known in the art that the pressurized fluidmay be introduced into the gap between the work piece and the ESC byholes (1710) or features that penetrate the ESC. It is known in the artthat any portion of the clamping electrode (2010) in the vicinity ofthis holes or any other feature that penetrates said electrode be cutaway. Typically, these holes (1710) or penetrating features are round innature; therefore, the cut-out within the electrode is typically of asimilar shape. A clearance (2015) between the hole (1710) or penetratingfeature and the clamping electrode (2010) cut-out is typically employedto prevent arcing or ionization of the pressurized fluid duringoperation. FIG. 15 further shows that for ESCs known in the art that thegas introduction holes (1710) are typically overlapped by the substrate(100). Furthermore, as shown in FIG. 18 in a prior art ESC the clampingelectrode (2010) has cut-outs some distance (2015) around the holes(1710) or penetrating features. Since the holes (1710) or penetratingfeatures are overlapped by the substrate, the cut-outs in the clampingelectrode are also overlapped by the substrate.

For etch processes that are ion driven (e.g., RF power is applied to thework piece support and/or ESC clamping electrode), the localizeddistortions in the electric field which arise from the discontinuitiesin a clamping electrode and/or work piece support can cause plasmasheath non-uniformities. The non-uniformities in the plasma sheath cancause ions to impinge on the wafer at various angles. The impinging ionswill have an angular distribution that is affected by several parameters(e.g., the work piece support RF frequency) which will be discussedbelow. The sheath distortions due to the discontinuities discussedabove, can skew, narrow or broaden the angular distribution. Whenetching features, these effects may translate to profiles which may betilted, skewed, bowed, or have sidewall degradation.

FIG. 17 shows another embodiment of the invention. When using a workpiece such as the one depicted in FIG. 3, or a substrate mounted to anoversized carrier in conjunction with an ESC (670) that extends past thesubstrate (100), it is preferred to place the holes (e.g., Helium gasinlet ports) (1710) outside the substrate (100) perimeter. Similarly, itis preferred that the lift pin holes (1720) are located outside thewafer (100) perimeter. In one embodiment (as shown in FIG. 9), the ESCcontains no penetrations for the lift mechanism (680). The liftmechanism (680) can be external to the work piece support (630). Note inFIG. 17, for illustration purposes, that the dashed line represents thearea of the ESC that the wafer (100) overlaps. During processing thework piece (320) (and consequently the substrate (100)) sits on the topsurface of the ESC (670).

As shown in FIG. 19, placement of the holes (e.g., He gas inlet ports)(1710) and lift pin holes (1720) outside the wafer perimeter allows theclamping electrode (2010) that is overlapped by the substrate (100) tobe continuous without cut outs (contrast to the prior art shown in FIG.18). In a preferred embodiment, the clamping electrode (2010) completelyoverlaps the substrate. In yet another embodiment, the clampingelectrode (2010) completely overlaps the substrate and overlaps a regionthat is greater than or equal to 1.02 times the substrate (100)diameter. In yet another embodiment, the clamping electrode (2010)overlaps the entire substrate (100) and extends at least 2 mm beyond theedge of the substrate (100). Preferably, the clamping electrode (2010)is at least approximately 40% larger than the substrate (100) diameter.

Although it is common to have holes (1710) and lift pin holes (1720)under the substrate for typical ESCs (see prior art FIGS. 15 and 16), itis preferable to not have them under the wafer when at least oneclamping electrode (2010) and/or the work piece support (630) is RFpowered. When using a work piece (320) and ESC such as the one depictedin FIG. 19, it is preferred that the diameter of the RF powered region(e.g., work piece support (630) or clamping electrodes (2010)) be largerthan the substrate (100) being etched. Sheath non-uniformities whicharise from the edge of the RF powered region can have detrimentaleffects on the etch profile as mentioned above, and thus it is preferredthat said RF powered region or regions be at least 5% larger than thediameter of the substrate (100). Ideally, if the thickness and relativedielectric constant is kept mostly unchanged above the RF powered regionor regions, the diameter of said RF powered regions should be about 40%larger than the substrate (100). The RF powered region can be greaterthan 10 mm beyond the perimeter of the substrate (100)

FIG. 26 shows another embodiment of the invention. In this embodimentthe ESC (670) overlaps the frame (310). In this configuration, there isa region of overlap between a seal band (1700) and the frame (310). Theframe (310) can completely overlap a seal band (1700). FIG. 26illustrates the case where the inner diameter of the frame (310) issmaller than the inner diameter of the outermost seal band (1700), it isimportant to note that the inner diameter of the outermost seal band(1700) can be smaller than or equal to the inner diameter of the frame(310). Furthermore, FIG. 26 shows an ESC configured for a single Heliumbackside cooling zone with a single seal band (1700), the invention canalso be beneficially applied to ESCs with multiple Helium cooling zonesand/or seal bands.

FIG. 26 also shows a work piece configuration where the flexible tape(300) (e.g., dicing tape) does not completely overlap the frame (310).In order to protect the seal band surface from degradation fromreactants or byproducts, it is preferred that a seal band (1700) doesnot extend past the perimeter of the flexible tape (300). In order toprovide a clamping force to the frame (310), it is also preferred thatsome portion of a clamping electrode (2010) overlap a portion of theframe (310). In this configuration, the frame (310) is in thermalcommunication with the temperature controlled work piece support (630),consequently, the frame (310) may be exposed to the plasma.

The embodiment shown in FIG. 26 can also benefit from features describedin previous embodiments—with the exception of the cover ring (660). Theembodiment illustrated and described by FIG. 26 can be beneficiallyapplied without the use of a cover ring.

For processes where an RF bias voltage is required, in order to minimizeperturbations in the plasma sheath at the substrate (100) surface thatmay lead to etch non-uniformities, it is preferred that the region ofthe ESC (670) overlapped by the substrate (100) be uniform with nopenetrations (e.g., Helium gas inlet holes (1710) or lift pin holes(1720)) through the ESC (670). It is preferred that the Helium gasinlets (1710) are not overlapped by the substrate (e.g., Helium gasinlets (1701) located outside the perimeter of the substrate (100)). TheHelium gas inlets (1710) must be located interior to the outer most sealband (1700). It is preferred that any seal band (1700) is not overlappedby the substrate (100). It is also preferred that the clamping electrode(2010) is continuous in the region where the clamping electrode isoverlapped by the substrate (100). It is preferred that the clampingelectrode (2010) completely overlaps the substrate (100). The clampingelectrode (2010) can extend beyond the perimeter of the substrate (100).It is further preferred that the lift pins (2025) and lift pin holes(1720) are located outside the substrate (100) perimeter. The lift pinscan touch the frame (310) and/or the tape (300) where the tape (300)overlaps the frame (310). In an alternate embodiment the lift mechanismcan be located outside the work piece support (630). The lift mechanismcan contact the frame (310) from the bottom, top, or side of the frame(310), or some combination of the three.

FIG. 27 shows yet another embodiment of the invention. This embodimentcan contain the features described in FIG. 26 with the addition of acover ring (660). In this configuration, the cover ring can overlap andprotect unclamped portions of the work piece (320) from the plasma. Thecover ring (660) is located between the plasma source (620) and the workpiece (320). The inner diameter of the cover ring (660) can be largerthan the inner diameter of the frame (310). The cover ring (660) canhave ports (1010) to allow increased pumping efficiency. It is preferredthat the ports (1010) are located outside the perimeter of the workpiece support (630).

It is also important to note that FIGS. 26 and 27 illustrate aspects ofthe invention for a work piece (320) that contains a single substrate(100). The invention can also be beneficially applied to a work piece(320) that contains multiple substrates (e.g., the work piece shown inFIG. 22).

In another embodiment of the invention, shown in FIG. 38, a cover ring(660) is configured for a work piece (320) that contains two or moresubstrates (100). The substrates (100) can be different sizes and/orshapes. A substrate (100) can be a piece of a larger substrate (100).The substrates (100) can contain different materials. It is preferredthat the substrates are processed with similar chemistries (e.g.,Silicon and Germanium both etch in Fluorine containing chemistries). Thecover ring (660) contains at least one opening (662) that exposes morethan one substrate (100) to a plasma. It is preferred that the coverring (660) does not overlap a substrate (100). In a preferredembodiment, the distance (3800) from the cover ring opening (662) to asubstrate (100) perimeter is at least 0.1 mm. It is further preferredthat the distance (3800) from the cover ring opening (662) to anysubstrate (100) perimeter is at least 0.1 mm. The distance (3800) canbetween a cover ring opening (662) and a substrate (100) perimeter canbe greater than 1 mm. The cover ring (660) can be in a different planethan at least one substrate (100). The cover ring (660) can be in adifferent plane than all the substrates (100). It is preferred that thecover ring (660) is not in contact with the work piece (320). While thecover ring (660) described in this embodiment is configured for multiplesubstrates, it can contain features described in previous embodiments ofcover ring (660).

In yet another embodiment of the invention, shown in FIG. 39, a coverring (660) is configured for a work piece (320) that contains two ormore substrates (100). The substrates (100) can be different sizesand/or shapes. A substrate (100) can be a piece of a larger substrate(100). The substrates (100) can contain different materials. It ispreferred that the substrates are processed with similar chemistries(e.g., Silicon and Germanium both etch in Fluorine containingchemistries). The cover ring contains at least two openings (663) thatallow plasma to contact at least one substrate (100). In a preferredembodiment, each opening (663) exposes one substrate (100) to a plasma.The openings (663) can be different sizes and shapes. It is preferredthat the cover ring (660) does not overlap a substrate (100). In apreferred embodiment, the distance (3900) from a cover ring opening(663) to a substrate (100) perimeter contained within the opening is atleast 0.1 mm. It is further preferred that the distance (3900) from acover ring opening (663) to any substrate (100) perimeter containedwithin the cover ring opening is at least 0.1 mm. The distance (3900)can between a cover ring opening (663) and a substrate (100) perimetercan be greater than 1 mm. The cover ring (660) can be in a differentplane than at least one substrate (100). The cover ring (660) can be ina different plane than all the substrates (100). It is preferred thatthe cover ring (660) is not in contact with the work piece (320). Whilethe cover ring (660) described in this embodiment is configured formultiple substrates, it can contain features described in otherembodiments of the cover ring described herein.

While FIGS. 26 and 27 show a work piece with the frame (310) and thesubstrate (100) located in the same plane (e.g., the same side of theflexible membrane (300), the work piece (320) can be configured suchthat the substrate (100) and the frame (310) are located on oppositesides of the membrane (300) (e.g., the bottom of the substrate isadhered to the top surface of the tape, while the top surface of theframe is adhered to the bottom surface of the tape). The concepts of thedescribed invention can be beneficially applied to this work piececonfiguration.

As shown in FIG. 20, an ESC (2330) consists of one or more electrodes(2340) to which a high voltage is applied. The potential difference canbe applied between at least one clamping electrode (2340) and anelectrically conductive surface (e.g., chamber wall (600)) in contactwith the plasma, or simply between two or more clamping electrodes.Typical applied clamping potentials range between 1 V and 10 kV, but theapplied clamping potential is preferably between 1 kV and 5 kV. For aclamped material (2320) exposed to plasma induced self-bias voltagesunder 2 kV, it is preferred that the applied clamping potentialdifference be greater than the plasma induced self-bias on the clampedmaterial (2320).

For all the embodiments of the invention described above, it ispreferred that the back side of the substrate (100) (e.g., the surfaceof the substrate opposite the surface that contains devices (110)) facethe flexible membrane (300) (e.g., the back of the substrate (100) canbe in contact with the flexible membrane (300)). In an alternateembodiment of the invention, the substrate (100) can be mounted on theflexible membrane (300) such that the surface of the substrate (100)that contains devices (110) is facing the flexible membrane (300) (e.g.,the device side of the substrate (100) can be in contact with theflexible membrane (300)).

As shown in FIG. 20, the clamping electrodes (2340) are separated fromthe work piece support (630) by an electrically insulating layer (2300)and separated from the material to be clamped (2320) by an upperelectrically insulating layer (2310). The thickness and relativedielectric constant of the upper electrically insulating layer (2310)above the ESC's clamping electrode is preferably chosen to minimize theimpact an insulating material to be clamped (2320) will have on theclamping performance (e.g., clamping force). In the current invention,the thickness of the dielectric (2310) and dielectric constant of saidlayer (2310) are chosen to both be higher than that of the materialbeing clamped (2320). It is not necessary for example that the ESC upperdielectric (2310) thickness and upper dielectric (2310) relativedielectric constant both be higher than that of the material to beclamped (2320), either parameter can be manipulated so that the productof the relative dielectric constant and the thickness of the ESC's upperdielectric layer (2310) is greater than product of the material to beclamped (2320) thickness and dielectric constant. The ratio of theproduct of upper dielectric insulator (2310) relative dielectricconstant with the upper dielectric insulator (2310) thickness to thatsame product for the material to be clamped (2320) is preferably greaterthan 1:1, but ideally greater than 5:1.

FIG. 21 shows another embodiment where the clamping electrode (2340) hasno electrical insulator interposed between the clamping electrode (2340)and the material to be clamped (2320). In the case where the ESCsclamping electrode (2340) is exposed (not covered by an electricalinsulator) and the clamping electrode (2340) is at least in partialcontact with the material to be clamped (2320), the bottom surface ofthe material to be clamped (2320) that is in contact with the ESCelectrode (2340) must be electrically insulating.

Typical ESCs known in the art consist of mainly dipole or monopoleelectrode configurations, but other multi-pole configurations arepossible. The electrode configuration can be chosen according to theapplication. In the case of clamping insulators, multipolar clampingelectrode configurations are typical; however, the dipole or multi-poleelectrode configurations can lead to charge separation on the bottomsurface of the work piece. This charge separation on the surface canlead to strong residual forces which can make the declamp routine longerand more complicated.

In the present invention, the ESC is optimized for clamping anddeclamping of electrically insulating materials, where the work piecesurface in contact with the ESC's top surface consists of an electricalinsulator. A monopole type ESC is used in order to facilitate thedeclamp routine. In the case of a monopole ESC, no lateral chargeseparation occurs on the bottom surface; instead, the bottom surface ismostly uniformly charged. Since the bottom surface of the work piece hasa mostly uniform charge distribution, the residual force will also bemostly uniform. This mostly uniform residual clamping force can beeasily canceled. Typically, a routine is employed to cancel the residualclamping force and declamp the work piece. In one routine, the appliedclamping voltage can be manipulated by setting said voltage to theplasma induced self-bias. In some cases the clamping voltage can be setto 0 V or an optimized set point of opposite polarity to the clampingvoltage polarity that was used to clamp the work piece. The declamproutines are typically executed after the work piece has been processed.

FIG. 8 shows a filler ring (700) that extends from the outer diameter ofthe ESC (670) to the lifting mechanism (680). This filler ring (700) isused to prevent the back surface of any exposed tape (300) from beingcontacted by the plasma. Although a separate filler ring (700) is shown,an extension of the ESC (670) would also prevent plasma exposure to thebackside of the tape (300). The filler ring (700) can be made of adielectric material, such as a ceramic (e.g., Aluminum Oxide) or aplastic material, (e.g., polytetrafluoroethylene (PTFE, Teflon))selected for both its low thermal conductivity and its low electricalconductivity. Although it is preferred to not directly expose theunclamped tape to plasma, some indirect exposure can be tolerated.

Typically during plasma processing, it is desirable to decouple the ionenergy and ion flux to achieve certain etch characteristics. Byemploying a powered work piece support and a high density source, suchas an ICP, mostly independent control of ion energy and flux can beachieved. The work piece support can be powered (e.g., biased) by a DCor AC power source. The AC bias frequency can range from a few kHz tohundreds of MHz. Low frequency typically refers to those biasfrequencies at or below the ion plasma frequency and high bias frequencyrefers to frequencies above the ion plasma frequency. The ion plasmafrequency is understood to depend on the atomic number of the ion, thusthe ion plasma frequency will be affected by the plasma chemistry. Suchchemistries can be Cl, HBr, I or F containing. In the case of SF₆containing plasmas, the ion plasma frequency is about 4 MHz. As shown inFIG. 24, when etching a substrate down to an interface, defined by thecontact of two materials (e.g., 2720 and 2730 in FIG. 24) of differentrelative dielectric constants (e.g., silicon on insulator, SOIstructures), problems with the etch associated with charging at theinterface, are well known. Such problems can be electrical or physicaland are commonly known as notching (e.g., see 2700 in FIG. 23),trenching, feature profile degradation. Interface examples where theseproblems typically occur are Silicon-on-Insulator (SOI), semiconductorsubstrate mounted on insulating carriers, semiconductor wafers (e.g.,GaAs, Si) mounted on tape, and substrates containing at least oneelectrically insulating layer. These problems are undesirable for deviceyield and performance. For example, when etching silicon using a timedivision multiplexed (e.g., TDM, DRIE or Bosch) process stopping on aninsulator (e.g., SiO₂) it is known in the art that undercut (ornotching) will occur at the silicon/insulator interface. As is wellknown in the art, such charging problems can be reduced by operating atlow RF bias frequencies (below the ion plasma frequency) andadditionally pulsing or modulating the RF bias power, as explained inU.S. Pat. No. 6,187,685. Note that the '685 patent teaches away from theuse of RF bias frequencies greater than the ion plasma frequency(approximately 4 MHz) for etching silicon with an insulating etch stop.

The present invention allows etching of these structures (e.g., SOI)using an RF bias frequency greater than the ion plasma frequency (e.g.,greater than approximately 4 MHz) when the high frequency RF bias isused in conjunction with the mechanical partition (690) between the highdensity plasma source (620) and the substrate (100). This configurationallows processing (e.g., etching) of the substrate (100) to proceedwhile still eliminating or reducing damage occurring at the interface(e.g., minimized notching (2700) at a silicon/exposed insulatorinterface). Preferably the RF bias frequency is 13.56 MHz (ISM band).

In one embodiment of the invention, the mechanical partition (690) isused in conjunction with a high frequency RF bias that is pulsed at somepoint during the process. The RF bias may be pulsed during the entireprocess. The pulsed RF bias can have at least two power levels in thepulse train—a high value and a low value. The pulsed RF bias may havemore than two RF bias power levels. The low value may be zero (no RFbias power). The pulsed RF bias levels can be changed continuously,discretely, or both. The RF bias frequency can also be greater thanapproximately 6 MHz up to approximately 160 MHz.

Equipment manufacturers have had to create unique configurations oftheir etch systems to support applications, such as but not limited tolow damage plasma etching and SOI applications, which cannot betypically used for other processes without added expense of multiplepower sources and/or matching networks, and sometimes electrostaticchucks. Power sources at a frequency of 13.56 MHz are common in theindustry due their availability and low cost. The invention makespossible the use of such power supplies to be used for the applicationscited above eliminating the need for added hardware and/or elaboratehardware configurations.

Since RF coupling at such low frequency is not efficient through a thickdielectric material, the RF coupling to the substrate (100) can be viathe one or more ESC clamping electrodes (2010), for example via acoupling capacitor rather than via the RF powered work piece support(630). To maintain uniform RF coupling to the substrate (100), the ESCelectrode or electrodes should also be uniformly disposed behind thesubstrate (100). This is difficult to achieve if multiple electrodes areused, since the necessary gaps between the electrodes result in a localvariation in the RF coupling which adversely affects the quality of theetch, particularly the undercutting at the substrate/tape interface. Apreferred embodiment of the ESC design therefore incorporates a socalled monopolar design, in which a single electrode is used to providethe clamping force.

The substrate can be processed using techniques well known in thesemiconductor industry. Silicon substrates are generally processed usinga Fluorine-based chemistry, such as SF₆. SF₆/O₂ chemistry is commonlyused to etch Silicon because of its high rate and anisotropic profile. Adisadvantage of this chemistry is its relatively low selectivity tomasking material for example to photoresist which is 15-20:1.Alternatively, a Timed Division Multiplex (TDM) process can be usedwhich alternates between deposition and etching to produce highlyanisotropic deep profiles. For example, an alternating process to etchSilicon uses a C₄F₈ step to deposit polymer on all exposed surfaces ofthe Silicon substrate (i.e., mask surface, etch sidewalls and etchfloor) and then an SF₆ step is used to selectively remove the polymerfrom the etch floor and then isotropically etch a small amount ofsilicon. The steps repeat until terminated. Such a TDM process canproduce anisotropic features deep into Silicon with selectivities to themasking layer of greater than 200:1. This then makes a TDM process thedesired approach for plasma separation of Silicon substrates. Note thatthe invention is not limited to the use of fluorine containingchemistries or a time division multiplex (TDM) process. For example,silicon substrates may also be etched with Cl, HBr or I containingchemistries as is known in the art.

For III-V substrates such as GaAs, a Chlorine based chemistry isextensively used in the semiconductor industry. In the fabrication ofRF-wireless devices, thinned GaAs substrates are mounted with the deviceside down onto a carrier, where they are then thinned and patterned withphotoresist. The GaAs is etched away to expose electrical contacts tothe front side circuitry. This well-known process can also be used toseparate the devices by the front side processing described in the abovementioned invention. Other semiconductor substrates and appropriateplasma processes can also be used for the separation of die in the abovementioned invention.

Many processes require an ion flux at the substrate (100) surface inorder achieve desired process results (e.g., GaAs etch, GaN etch, SiO₂etch, SiC etch, quartz etch, etc.) For the case where the substrate(100) is part of a work piece (320), the ion flux and/or ion energyrequired to process the substrate (100) can often be high enough todamage portions of the work piece (e.g., the flexible membrane (300)) orenable undesirable side reactions—making it important to protectportions of the work piece from the plasma. In contrast, in order toimprove the process results (e.g., uniformity, electrostatic clampingperformance, etc.), it can be desirable to provide some portion of thework piece that lies outside the perimeter of the substrate with contactto the plasma—though at a lower ion flux and/or ion energy thanexperienced by the substrate (100). What is needed is means to adjustthe exposure of different portions of the work piece (320) to differentplasma ion fluxes and/or ion energies.

As shown in FIG. 28, another embodiment of the invention is a modifiedcover ring (2830) that contains at least one perforated region (2800)that allows a path from the plasma to the work piece where the workpiece is overlapped by the perforated region (2800). The perforatedregion (2800) can overlap the flexible membrane (300). The perforatedregion (2800) can overlap the frame (310). The perforated region (2800)can extend beyond the work piece (320). The perforated region (2800) canattenuate the ion flux from the plasma to a portion of the overlappedarea of the work piece (e.g., the area of the work piece overlapped bythe perforated region (2800) and outside the perimeter of the substrate)by at least 10%. In a preferred embodiment the perforated region (2800)can attenuate ion flux from the plasma to a portion of the work pieceoverlapped by the perforated region (2800) by at least 30%. It ispreferred that the perforated region (2800) does not overlap thesubstrate (100). In one embodiment, as shown in FIG. 29, the modifiedcover ring (2830) and substrate (100) are located in different planes(e.g., non-coplanar). Therefore the inner periphery of the cover ring(2831) is not adjacent to the outer periphery (101) of the substrate.

The modified cover ring (2830) typically contains a cover ring opening(2820) where the substrate (100) is not overlapped by the modified coverring (2830). The cover ring opening (2820) can range from greater thanapproximately 0.1 mm to less than approximately 20 mm larger than thesubstrate diameter, with a preferred value between 1 mm and 4 mm.Preferably the cover ring opening (2820) is 2 mm larger than thesubstrate (100) diameter. It is preferred that the plasma ion density atthe substrate (100) surface is greater than the plasma ion density atthe work piece (320) surface where it is overlapped by the modifiedcover ring (2830).

In some cases it can be desirable to have plasma present in the regionbetween some portion of the perforated region (2800) of the modifiedcover ring (2830) and the work piece that is overlapped by theperforated region (2800) of the modified cover ring (2830). (e.g., itcan be desirable to allow plasma underneath the modified cover ring(2830) when using a monopolar ESC to clamp the work piece in someportion of the area overlapped by the modified cover ring (2830). In oneembodiment, in order to allow plasma to penetrate the volume between themodified cover ring (2830) and the work piece (320), the distancebetween the bottom surface of the perforated region of the cover ringand the top surface of the work piece (320) can be between 1 mm and 5cm.

The modified cover ring (2830) can contain at least one region (2810)that is non-perforated. The non-perforated region (2810) of the modifiedcover ring (2830) can prevent the plasma from contacting the work piecewhere the non-perforated region (2810) overlaps the work piece (320). Itis preferred that the plasma ion density at the work piece (320) surfaceis greater where it is overlapped by a perforated region (2800) isgreater than the plasma ion density at the work piece (320) surfacewhere it is overlapped by a non-perforated region (2810). It is alsopreferred that the plasma density at the work piece (320) surface at thesubstrate (100) is greater than the plasma density at the work piecesurface overlapped by the perforated region(s) (2800) of the modifiedcover ring (2830) which in turn is greater than the plasma density atthe work piece (320) surface overlapped by the non-perforated region(s)(2810) of the modified cover ring (2830). The plasma density under thenon-perforated region of the modified cover ring (2830) can be zero.

FIG. 29 shows a cross sectional view of a modified cover ring (2830)with a perforated region (2800). The modified cover ring (2830) cancontain pumping ports (1010) to improve the system conductance. It ispreferred that the pumping ports (1010) are located outside theperimeter of the work piece (320). The pumping ports can be located inthe perforated region (2800) of the modified cover ring (2830), thenon-perforated region (2810), or both. It is preferred that the pumpingports (1010) do not overlap the work piece (320).

In a preferred embodiment, the perforated region (2800) of the modifiedcover ring (2830) overlaps a portion of the work piece (320) that isoverlapped by an ESC clamping electrode (2010). The perforated region(2800) of the modified cover ring (2830) can overlap all areas of thework piece (320) that are not overlapped by the substrate but areoverlapped by an ESC clamping electrode (2010). All of the perforatedregion (2800) can be overlapped by an ESC clamping electrode (2010). Itis also preferred that the perforated region (2800) of the modifiedcover ring (2830) does not overlap portions of the work piece (320) thatare not in thermal contact with the work piece support (630) (e.g., theperforated region (2800) of the modified cover ring (2830) does notoverlap portions of the work piece (320) that are not clamped by theelectrostatic chuck (670), perforated region (2800) of the modifiedcover ring (2830) does not overlap portions of the work piece (320)outside the outermost ESC seal band (1700)).

The perforations in the perforated region (2800) can be any size andshape. The perforation sizes and shapes can be variable or uniformwithin or between perforated region(s) (2800). The spacing of theperforations can be uniformly or variably distributed within or betweenperforated region(s) (2800).

While the modified cover ring (2830) shown in FIG. 29 is illustratedwith a constant thickness—the cover ring thickness can vary within thering (e.g., thickness variation as a function of radius or thicknessvariation across the ring). The thickness of a perforated region (2800)can be different from the thickness of a non-perforated region (2810).The thickness of a perforated region (2800) can be thinner than thethickness of a non-perforated region (2810).

FIG. 30 shows another embodiment of the invention. This embodimentincludes the elements described and illustrated in FIG. 29.Additionally, in this embodiment, a perforated region (2800) of themodified cover ring (2830) is not coplanar with a non-perforated region(2810) of the modified cover ring (2830). In a preferred embodiment, thedistance between a perforated region (2800) and the work piece (320) isgreater then a distance between the non-perforated region (2810) and thework piece (320). The cover ring (2830) can be comprised of two or morepieces.

In another embodiment of the invention, shown in FIG. 40, a modifiedcover ring (2830) is configured for a work piece (320) that contains twoor more substrates (100). The modified cover ring (2830) contains atleast one perforated region (2800). The modified cover ring (2830) cancontain a non-perforated region (2810). The substrates (100) can bedifferent sizes and/or shapes. A substrate (100) can be a piece of alarger substrate (100). The substrates (100) can contain differentmaterials. It is preferred that the substrates are processed withsimilar chemistries (e.g., Silicon and Germanium both etch in Fluorinecontaining chemistries). The modified cover ring (2830) contains atleast one opening (2820) that exposes more than one substrate (100) to aplasma. It is preferred that the modified cover ring (2830) does notoverlap a substrate (100). In a preferred embodiment, the distance(3800) from the modified cover ring opening (2820) to a substrate (100)perimeter is at least 0.1 mm. It is further preferred that the distance(3800) from the modified cover ring opening (2820) to any substrate(100) perimeter is at least 0.1 mm. The distance (3800) can between amodified cover ring opening (2820) and a substrate (100) perimeter canbe greater than 1 mm. The modified cover ring (2830) can be in adifferent plane than at least one substrate (100). The modified coverring (2830) can be in a different plane than all the substrates (100).It is preferred that the modified cover ring (2830) is not in contactwith the work piece (320). While the modified cover ring (2830)described in this embodiment is configured for multiple substrates, itcan contain features described in other embodiments of the cover ringdescribed herein.

In yet another embodiment of the invention, shown in FIG. 41, a modifiedcover ring (2830) is configured for a work piece (320) that contains twoor more substrates (100). The modified cover ring (2830) contains atleast one perforated region (2800). The modified cover ring can containa non-perforated region (2810). The substrates (100) can be differentsizes and/or shapes. A substrate (100) can be a piece of a largersubstrate. The substrates (100) can contain different materials. It ispreferred that the substrates are processed with similar chemistries(e.g., Silicon and Germanium both etch in Fluorine containingchemistries). The modified cover ring (2830) contains at least twoopenings (2820) that allow plasma to contact at least one substrate(100). In a preferred embodiment, each modified cover ring opening(2820) exposes one substrate (100) to a plasma. The modified cover ringopenings (2820) can be different sizes and shapes. It is preferred thata modified cover ring (2830) does not overlap a substrate (100). In apreferred embodiment, the distance (3900) from a modified cover ringopening (2820) to a substrate (100) perimeter contained within thatopening is at least 0.1 mm. It is further preferred that the distance(3900) from a cover ring opening (2820) to any substrate (100) perimetercontained within that opening is at least 0.1 mm. The distance (3900)between a modified cover ring opening (2820) and a substrate (100)perimeter can be greater than 1 mm. The modified cover ring (2830) canbe in a different plane than at least one substrate (100). The modifiedcover ring (2830) can be in a different plane than all the substrates(100). It is preferred that the modified cover ring (2830) is not incontact with the work piece (320). While the modified cover ring (2830)described in this embodiment is configured for multiple substrates, itcan contain features described in other embodiments of the cover ringherein.

In some cases, it can be beneficial to add an intermediate ring (4200)to a work piece (4210) as shown in FIG. 42. The intermediate ring canhave at least one opening. The intermediate ring opening can be largerthan the substrate (100). The intermediate ring (4210) can beassymetrically shaped. The intermediate ring (4200) can be in contactwith the tape (300). The tape (300) can be a UV release tape as is knownin the art. The intermediate ring (4200) can be rigid. The intermediatering (4200) can be interposed in the region between the outer peripheryof the substrate (100) and the inner edge of the rigid frame (310). Theinner diameter of the intermediate ring (4200) can be greater than thesubstrate (100) diameter. In a preferred embodiment, the intermediatering (4200) does not overlap the substrate (100). The outer diameter ofthe intermediate ring can be less than the inner diameter of the rigidframe (310). one surface of the intermediate ring (4200) and one surfaceof the substrate (100) can be coplanar. The intermediate ring (4200) canbe comprised of one or more pieces. When the intermediate ring (4200) iscomprised of two or more pieces, the intermediate ring assembly can becontinuous or contain at two or more discrete sections.

In another embodiment, at least some portion of the intermediate ring(4200) overlaps at least some portion of the substrate (100). In thisembodiment, the inner diameter of the intermediate ring can be less thanthe diameter of the substrate (100). The intermediate ring can contactthe substrate (100).

In an alternate embodiment, the intermediate ring (4200) overlaps someportion of the substrate (100), where the intermediate ring (4200) doesnot contact the substrate (100) in at least some portion of theintermediate ring/substrate overlapped region. The inner diameter of theintermediate ring can be less than the diameter of the substrate (100).

In yet another embodiment, at least some portion of the intermediatering overlaps some portion of the substrate and there is no contactbetween the intermediate ring (4200) and the substrate (100). Theintermediate ring can contact the substrate (100). In embodiments wherethe intermediate ring (4200) overlaps the substrate, the intermediatering (4200) can be used to reduce the exposure of the overlapped regionof the substrate to the plasma. The intermediate ring can be used toprevent a portion of the substrate from being exposed to the plasma.

In another embodiment, the intermediate ring (4200) overlaps at leastsome portion of the rigid frame (310). In yet another embodiment, theintermediate ring (4200) can be attached to the rigid frame (310). Theattachment between rigid frame (310) and the intermediate ring (4200)can be reversible. (e.g., an intermediate ring (4200) is attached to therigid frame (310) prior to plasma processing and then detached from therigid frame (310) after the plasma process has been completed)

The intermediate ring (4200) can be located on the same side of the tape(300) as the rigid frame (310). The intermediate ring (4200) can belocated on the same side of the tape (300) as the substrate (100). Inone embodiment, the intermediate ring (4200) is used to reduce the areaof tape (300) exposed to the plasma.

The intermediate ring (4200) can be the same thickness as the rigidframe (310) or the substrate (100). The intermediate ring (4200) can befabricated from a number of materials including metals, semiconductors,and dielectric materials including ceramics and plastics. Theintermediate ring (4200) can be comprised of more than one material(e.g., a ceramic layer over a metal layer). The intermediate ring (4200)can be constructed from the same material as the rigid frame (310).

FIG. 43 shows a work piece containing an intermediate ring (4200) on awork piece support (630). The intermediate ring (4200) in FIG. 43 doesnot overlap the cover ring (660) and will be exposed to the plasmaduring the plasma processing of the substrate (100). In cases where theintermediate ring (4200) is exposed to the plasma, it is preferred thatthe ring (4200) is made of a plasma resistant material (e.g.,ceramics—including aluminum oxide, aluminum nitride, yttrium containingmaterials, silicon carbide, etc.).

In another embodiment, a portion of the intermediate ring (4200) canoverlap the cover ring (660). In yet another embodiment, theintermediate ring (4200) is completely overlapped by the cover ring(660).

Some portion of the intermediate ring (4200) can overlap some portionelectrostatic chuck clamping electrodes (2010). The electrostaticclamping electrodes (2010) can completely overlap the intermediate ring(4200). The intermediate ring (4200) can overlap at least a portion ofthe electrostatic chuck sealing region (1700).

The intermediate ring (4200) can be applied to the work piece prior toplasma processing. The intermediate ring can be added to the work piece(4210) within the process chamber (600).

FIG. 44 shows yet another embodiment of the invention with anintermediate ring (4200) as part of a work piece (4210). This embodimentcontains features listed for the intermediate ring (4200) for FIGS. 42 &43 except in this embodiment there is no cover ring (660) between theplasma and the work piece (4210). In this embodiment, it is preferredthat the intermediate ring (4200) is in thermal communication with thework piece support (630) e.g., at least some portion of the tape (300)overlapped by the intermediate ring (4200) is clamped by theelectrostatic chuck clamping electrode(s) (2010).

FIG. 45 shows a further embodiment of the invention. In this embodiment,a work piece (4210) is assembled that contains a rigid frame (310), anintermediate ring (4200), a flexible membrane (300) (e.g., tape), and atleast one substrate (100). The work piece (4210) is loaded into aprocessing chamber (600). The substrate (100) is exposed to a plasma.Once the substrate (100) has been at least partially processed, the workpiece (4210) is modified by removing the rigid frame (310). The modifiedwork piece (without the rigid frame (310)) is then sent downstream forfurther processing. One example of this embodiment would be assembling awork piece consisting of a dicing frame for a 200 mm wafer (rigidframe), a dicing frame for a 150 mm wafer (intermediate ring), dicingtape (flexible membrane), and a 150 mm wafer (substrate). In thisexample the work piece can be processed in a plasma chamber configuredfor a 200 mm compatible dicing frame. After the plasma process, the 200mm frame can be removed (to form the modified work piece), leaving the150 mm wafer taped to a 150 mm dicing frame. The 150 mm wafer and frame(modified work piece) can then be further processed downstream on 150 mmcompatible processing equipment.

While the intermediate ring (4200) shown in FIGS. 42, 43, and 44 isconfigured for a single substrate. The embodiments shown in thesefigures can also be beneficially applied to a work piece (4210) thatcontains two more substrates (100). In an embodiment where anintermediate ring (4200) is used in conjunction with multiple substrates(100), the work piece (4210) can contain one or more intermediate rings(4200). The intermediate rings (4200) can be the same size and shape ordifferent sizes and shapes.

The invention described in FIG. 45 can also be beneficially applied towork pieces (4210) that contain two or more substrates (100).

To further reduce the problems associated with charging at thesubstrate/tape interface, the process can be changed at the point atwhich the interface is exposed to a second process which has lesstendency to undercut and is typically a lower etch rate process. Thepoint in time at which the change takes place depends upon the substratethickness, which is likely to vary. To compensate for this variability,the time at which the substrate/tape interface is reached is detectedusing an endpoint technique. Optical techniques which monitor the plasmaemission are commonly used to detect endpoint and U.S. Pat. Nos.6,982,175 and 7,101,805 describe such an endpoint technique which isappropriate to a TDM process.

FIG. 31 illustrates issues that can arise during a die singulationprocess using plasma processing. FIG. 31 a shows a typical pattern ofdie (110) on a wafer (not shown) separated by street regions (120). Theplasma dicing process typically follows a chemically assisted etchmechanism, where the etch rate of the exposed materials is in part afunction of the concentration of available reactants. For the case ofSilicon in a Fluorine-containing plasma (e.g., SF₆ plasma), the etchrate is typically a function of free Fluorine (e.g., SF₆ partialpressure, SF₆ mass flow rate, etc.). In a process following achemically-assisted etch mechanism, two regions of identical area (3120,3130) can etch at different rates due to their local environment (e.g.,aspect ratio). Aspect ratio can be defined as a feature's depth dividedby its smallest lateral dimension (length or width). Higher aspect ratiofeatures typically etch slower—particularly for chemically drivenprocesses. For example, while etch regions 3120 and region 3130 are thesame area, the street intersection region (3120) will have a lowereffective aspect ratio and typically etch faster than street region(3130). This faster etch rate can result in undesirable feature profilesand/or can damage the underlying tape (e.g., damage tapestretchability).

FIG. 32 shows yet another embodiment of the invention. By adding maskedetch assist features (3200) that protect portions of the streetintersection region (3120) from etching, the effective aspect ratio ofthe street intersection regions (3120) can be increased—decreasing thelocal etch rate in the street intersection region (3210) to a valuesimilar to the surrounding street regions (3130). The etch assistfeatures (3200) can be patterned using methods known in the art, usingany mask material that has a suitable etch resistance (e.g.,polymers—including polyimides and photoresists; dielectrics—includingSiO₂, SiN, Al₂O₃, AlN; carbon containing materials—including carbon anddiamond like carbon (DLC); and metals—including Al, Cr, Ni, etc.). Themask material of an etch assist feature (3200) can be the same materialused to mask the die (110) during the plasma dicing process. When morethan one etch assist feature (3200) is present, the etch assist features(3200) can be patterned using more than one masking material. A singleetch assist feature (3200) can be patterned using more than one maskmaterial within the etch assist feature (3200). It is preferred that theetch selectivity of the etch assist feature (3200) mask material to thestreet material to be removed is at least 10:1. It is further preferredthat the etch resistance is of the mask material is greater than 50:1.It is preferred that etch assist features (3200) are separated from thedie (110) after the plasma dicing process. It is desirable for the etchassist features (3200) to remain intact during plasma dicing and/ordownstream operations (e.g., etch assist features do not break orcontact a die (110)). It is preferred that the etch assist features(3200) remain adhered to the tape (300) during the plasma dicingprocess. It is preferred that a singluated etch assist feature (3200)does not contact a die (110).

Etch assist features (3200) can be patterned into a wide array of shapesincluding polygons, squares, rectangles, and/or quadrilaterals. The etchassist features (3200) can contain curves or rounded features. The etchassist features (3200) can be circular or oval. The etch assist features(3200) can be composed of more than one smaller feature (see etch assistfeature group (3201) for example).

In order to cleanly separate the die (110) during the singulationprocess, it is preferred that an etch assist feature (3200) is notconnected to a die (110). In a preferred embodiment, none of the etchassist features (3200) are connected to a die (110).

The etch assist features (3200) can be connected to one another. Theetch assist features (3200) can be uniform or variable size and shapeacross the wafer. For the case where the die (110) or streets (120) varyacross a wafer, it is preferred that the etch assist feature (3200) sizeand/or shape also varies across the wafer. While FIG. 32 illustrates theinvention in use with rectangular die (110), the invention can bebeneficially applied to die of different shapes including die withrounded corners.

FIG. 31 b shows a prior art pattern of die (110) that contains a processcontrol monitor (PCM) structure (3100). PCM structures (3100) can beused to check the quality of the devices during the device fabricationprocess. PCM structures (3100) are typically not yieldable die andconsume substrate real estate that might otherwise be available foruseful die. Since PCM structures (3100) are typically not incorporatedinto final product die, PCM structures (3100) are typically located inthe dicing street regions (120) of the wafer. The number and size of thePCM structures (3100) is typically a function of the chip design andfabrication processes. In the prior art, in order to keep the PCMstructures (3100) separate from the useful die (110), it is oftennecessary to increase the width of the PCM street (3110) around the PCMstructures (3100). These wider PCM street regions (3110) can beundesirable for two reasons: firstly, street regions of different widthscan etch at different rates (e.g., wider streets etch faster)potentially causing undesirable variability in die sidewall; andsecondly, wider street regions (110) represent wasted area of thesubstrate that potentially can be used to fabricate additional devices(110).

FIG. 33 shows yet another embodiment of the invention to present a moreuniform pattern load to the plasma. In this embodiment, PCM assistfeatures (3300) are added to a PCM street region (3110) to reduce thearea of exposed substrate in a PCM street region (3110). By reducing theexposed substrate area, PCM assist features (3300) can reduce the etchrate of the exposed substrate locally near a PCM assist feature (3300)to an etch rate similar to the etch rate in a street (120) between twodie (110). In a preferred embodiment, the width (3330) of exposed (e.g.,unmasked) material between a die (110) and a PCM assist feature (3300)is similar to the width of a street region (120). A PCM assist feature(3300) can be connected to/or touch the PCM structure (3100). A PCMassist feature (3300) can be separated from a PCM structure (3100) by agap (3310). The gap (3310) between a PCM assist feature (3300) and a PCMstructure (3100) can be less than or equal to a street (120) width.

If a PCM assist feature (3300) was patterned to be substantiallycontinuous across a substrate, the continuous PCM assist feature couldpotentially inhibit the uniform stretching of the tape (300) afterplasma dicing—adversely affecting downstream operations. In oneembodiment, an area of a PCM street (3110) that is to be protected frometching is protected by more than one PCM assist feature (3300). It ispreferred that a PCM assist features (3300) be separated from adjacentdie (110) after plasma dicing. The PCM assist features (3300) can beseparated from one another after the plasma dicing process. A PCM assistfeature (3300) can be separated from another PCM assist feature (3300)by a tape stretch gap (3320). It is preferred that at least one PCMassist feature (3300) is separated at a tape stretch gap (3320) duringthe plasma dicing process (e.g., the substrate material between at leastone pair of adjacent PCM assist features (3300) is removed to expose anunderlying layer. This underlying layer can be the work piece tape (300)or a thin film or film stack on the back of the substrate—the thin filmcan be a wafer back metal layer as is known in the art. This tapestretch gap allows for more uniform stretching of the dicing tape (300)during downstream pick and place operations. It is preferred that thewidth of the tape stretch gap (3320) is similar to the street (120)width (e.g., tape stretch gap in the range of approximately 5 to 30microns in width). The PCM assist features (3300) can have one lateraldimension approximately the same as a die (110) dimension (e.g., dielength or width).

The PCM assist features (3300) can be patterned using methods known inthe art, using any mask material that has a suitable etch resistance(e.g., polymers—including polyimides and photoresists,dielectrics—including SiO₂, SiN, Al₂O₃, AlN, carbon-containingmaterials—including carbon and diamond like carbon (DLC), andmetals—including Al, Cr, Ni, etc.). The mask material of the PCM assistfeature(s) (3300) can be the same material used to mask the die (110)during the plasma-etch process. It is preferred that the etchselectivity of the PCM assist feature (3300) mask material to the streetmaterial to be removed is at least 10:1. It is further preferred thatthe etch resistance (e.g., etch selectivity) of the mask material to thestreet material is greater than 50:1. When more than PCM assist feature(3300) is present, the PCM assist features (3300) can be patterned usingdifferent one masking materials. A single PCM assist feature (3300) canbe patterned using more than one mask material within the PCM assistfeature (3300).

FIG. 34 shows another embodiment of the invention. Unlike conventionaldicing saws, plasma dicing does not require linear street regions (120)between die (110) across the entire substrate. In order to present amore uniform etch load to the plasma, it is preferred to shift groups ofdie (3400) near the PCM structure (3100) such that the width of thedicing street (3410) near the PCM structure (3100) is similar to thewidth of a standard dicing street (120) region (e.g., PCM street width(3410) of approximately 5 to 30 microns in width).

FIG. 35 shows yet another embodiment of the invention. FIG. 35 shows die(110) with rounded corners. These rounded corners create a larger areaat the intersection of dicing streets (120) as compared to rectangulardie known in the art. In order to make use of this extra exposed areabetween die (110), modified PCM structures (3500) can be placed withinthe intersection of dicing streets (120). Modified PCM structures (3500)can have the same functionality as PCM structures (3100) known in theart. These modified PCM structures (3500) can be various sizes andshapes (e.g., rectilinear, rounded or other shapes). The modified PCMstructure (3500) can retain test functionality after plasma dicing. Itis preferred that the modified PCM structures (3500) are singulated fromthe die during the plasma dicing process. (e.g., the substrate materialbetween at least one die and a modified PCM structure (3500) is removedto expose an underlying layer. This underlying layer can be the workpiece tape (300) or a thin film or film stack on the back of thesubstrate—the thin film can be a wafer back metal layer as is known inthe art). It is preferred that the modified PCM structure (3500) nottouch any of the die (110). While FIG. 35 illustrates die with roundedcorners, the invention can be beneficially applied to die with any shapeperimeter (e.g., rectangular or square die).

FIG. 36 illustrates another issue that can arise during a diesingulation process using plasma processing. FIG. 36 shows a typicalpattern of die (110) on a wafer (100) separated by street regions (120).The plasma dicing process typically follows a chemically assisted etchmechanism, where the local etch rate of the exposed materials can be inpart a function of amount nearby exposed material (e.g., etch loadingeffect). Features near large exposed areas of substrate (100) typicallyhave lower etch rates. In some die pattern layouts there can be an edgeregion (3620) of exposed wafer between an edge of an outermost die(3600) and the perimeter of the substrate (100) (e.g., the substratearea between the dotted line 3625 and the perimeter of the substrate(100)). During a plasma dicing process an edge region can etch at asignificantly different rate than a street region (120). This differencein etch rate between the edge region (3620) and a street region (120)can result in undesirable feature profiles, damage the underlying tape,or longer plasma dicing process time.

FIG. 37 shows yet another embodiment of the invention. By adding maskedload assist features (3700) that protect portions of the edge region(3620) of the substrate (100) from etching, the effective load (e.g.,exposed substrate area) can be reduced—allowing the local etch rate inan exposed area (3730) of an edge region (3620) to attain a valuesimilar to an etch rate in an adjacent street regions (120). The loadassist features (3700) can be patterned using methods known in the art,using any mask material that has a suitable etch resistance (e.g.,polymers—including polyimides and photoresists; dielectrics—includingSiO₂, SiN, Al₂O₃, AlN; carbon containing materials—including carbon anddiamond like carbon (DLC); and metals—including Al, Cr, Ni, etc.). Themask material of a load assist feature (3700) can be the same materialused to mask the die (110) during the plasma dicing process. When morethan one load assist feature (3700) is present, the load assist features(3700) can be patterned using more than one masking material. A singleload assist feature (3700) can be patterned using more than one maskmaterial within the load assist feature (3700). It is preferred that theetch selectivity of the load assist feature (3700) mask material to theexposed material (e.g., substrate) to be removed is at least 10:1. It isfurther preferred that the etch selectivity of the exposed material tothe load assist feature mask material is greater than 50:1.

It is desirable to have a pattern gap (3710) between a die and anadjacent load assist feature. The pattern gap (3710) can be the samewidth as a street (120). One material in the pattern gap (3710) has beenremoved during plasma dicing, it is preferred that a load assist feature(3700) be separated from an adjacent die (110) (e.g., the substratematerial between at least one die and a load assist feature (3700) isremoved to expose an underlying layer. This underlying layer can be thework piece tape (300) or a thin film or film stack on the back of thesubstrate—the thin film can be a wafer back metal layer as is known inthe art). A load assist feature (3700) can be separated from an adjacentload assist feature (3700) after the plasma dicing process. Adjacentload features can be separated from one another by a load assist featuregap (3720). This load assist feature gap (3720) allows for more uniformstretching of the dicing tape (300) during downstream pick and placeoperations. It is preferred that the width of the load assist featuregap (3720) is similar to the street (120) width (e.g., tape stretch gapin the range of approximately 5 to 30 microns in width). The width ofthe load assist feature gap (3720) can be similar to the pattern gap(3710). A load assist feature (3700) can have one lateral dimensionapproximately the same as a die (110) dimension (e.g., die length orwidth). In order to help with any downstream tape stretch operation, itis desirable to have at least one gap (e.g., load assist feature gap(3720), pattern gap (3710), etc.) or street (120) intersect theperimeter of the wafer.

Some wafers, as is known in the art, have an edge bead removed region atthe perimeter of the wafer such that the top surface of the substratenear the perimeter is exposed substrate material. In another embodiment,for wafers that have been edge bead removed, it is desirable to have atleast one gap (e.g., load assist feature gap (3720), pattern gap (3710),etc.) or street (120) connected to the edge bead removed region (e.g.,so that there is at least one area of continuous exposed substrate fromthe perimeter of the wafer to at least one gap).

It is desirable for the load assist features (3700) to remain intactduring plasma dicing and/or downstream operations (e.g., load assistfeatures do not break or contact a die (110)). It is preferred that theload assist features (3700) remain adhered to the tape (300) during theplasma dicing process. It is preferred that a singluated load assistfeature (3700) does not contact a die (110).

Load assist features (3700) can be patterned into a wide array of shapesincluding polygons, squares, rectangles, and/or quadrilaterals. The loadassist features (3700) can contain curves or rounded features. The loadassist features (3700) can be circular or oval. The load assist features(3700) can be composed of more than one smaller feature.

In order to cleanly separate the die (110) during the singulationprocess, it is preferred that a load assist feature (3700) is notconnected to a die (110). In a preferred embodiment, none of the loadassist features (3700) are connected to a die (110).

A load assist feature (3700) can be connected to another load assistfeature (3700). The load assist features (3700) can be uniform orvariable size and shape across the wafer. For the case where the die(110) or streets (120) vary across a wafer, it is preferred that theload assist feature (3700) size and/or shape also varies across thewafer. While FIG. 37 illustrates the invention in use with rectangulardie (110), the invention can be beneficially applied to die of differentshapes including die (110) with rounded corners.

Note that while the previous examples describe etch assist features(3200), PCM assist features (3300), modified PCM structures (3500), andload assist features (3700) individually, that any combination of theseelements can be beneficially applied.

After singulation of the semiconductor substrate, there can be unwantedresidues that exist on the devices. Aluminum is commonly used as anelectrical contact for semiconductor devices and when exposed toFluorine based plasmas a layer of AlF₃ is formed on its surface. AlF₃ isnonvolatile under normal plasma processing conditions and is not pumpedaway from the substrate and out of the system and remains on the surfaceafter processing. AlF₃ on Aluminum is a common cause of failure fordevices because the bonding strength of wires to the electrical contactsis greatly reduced. Thus, the removal of the AlF₃ from the surface ofthe electrical contacts after plasma processing is important. Wetmethods can be used; however, this becomes difficult because of thefragile nature of the separated die, and the possible damage to the tapecausing die release. Therefore, the process can be changed to a thirdprocess while the substrate is still within the vacuum chamber, to aprocess designed to remove any AlF₃ formed. U.S. Pat. No. 7,150,796describes a method for in-situ removal of AlF₃ using an Hydrogen basedplasma. Likewise, an in-situ treatment can be used to remove otherhalogen-containing residues when other halogen-containing gases are usedto etch the substrate.

While the above examples discuss the use of plasma for separating die(dicing), aspects of the invention may be useful for relatedapplications such as substrate thinning by plasma etching. In thisapplication the substrate (100) can be have some features on the surfaceto be etched or alternatively the surface to be etched may befeatureless (e.g., thinning the bulk substrate).

The present disclosure includes that contained in the appended claims,as well as that of the foregoing description. Although this inventionhas been described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

Now that the invention has been described,

What is claimed is:
 1. A method for plasma processing a substrate, themethod comprising: providing a process chamber having a wall; providinga plasma source adjacent to the wall of the process chamber; providing awork piece support within the process chamber; placing the substrateonto a carrier support film on a frame to form a work piece; providingan intermediate ring interposed between the substrate and the frame;loading the work piece onto the work piece support; generating a plasmathrough the plasma source; and etching the work piece through thegenerated plasma while a portion of the support film is exposed to thegenerated plasma.
 2. The method according to claim 1 wherein theintermediate ring contacts the support film.
 3. The method according toclaim 1 further comprising: the intermediate ring having an innerdiameter; and the substrate having an outer diameter; wherein the innerdiameter of the intermediate ring being greater in size than the outerdiameter of the substrate.
 4. The method according to claim 1 whereinthe intermediate ring being positioned coplanar with the substrate. 5.The method according to claim 1 wherein the intermediate ring furthercomprising one or more pieces.
 6. The method according to claim 1further comprising: the support film having an upper surface and a lowersurface; and the intermediate ring being positioned on the upper surfaceof the support film, and the substrate being positioned on the uppersurface of the support film.
 7. A method for plasma dicing a substrate,the method comprising: assembling a work piece having a rigid frame, anintermediate ring, a flexible membrane, and at least one substrate;transferring said work piece into a processing chamber; exposing thesubstrate of said work piece to a plasma while a portion of the flexiblemembrane is exposed to said plasma; modifying said work piece byremoving the rigid frame; and processing said modified work piece.